Cleanup: set the base in the setting templates, instead of defining the base for every setting

This has the added benefit of not getting mistaken that multiple bases can be used for the same SettingTable

Codechange: use initializer_lists for the settings tables

Not using vectors as those require copying from the initializer list and that
makes unique_ptrs to the actual SettingDesc objects later impossible.

Change: [Network] Update server's NetworkServerGameInfo only when needed

Split the updating in a "static" version that only needs to be called when a new map is loaded or some settings are changed, and a "dynamic" version that updates everything that changes regularly such as the current game date or the number of spectators.

Codechange: use NetworkAddress instead of two host/port variables where possible

This also means we no longer need last_host/last_port, but can
just use a single last_joined setting.

Remove: "language" field from server/client

The original idea was that people could find a server they could
talk in their native language on. This isn't really used in that
way. There are several reasons for removing this:

- the client also sends his "language" to the server, but nothing
is doing anything with this.
- flags are a bad way to represent languages, and over the years
we had several (rightfully) complaints about this.
- most servers have their language set to "All", and prefix the
servername with the language it is about. This is a much more
efficient way to do the same.

All in all, this feature should go back to the drawing board.
Maybe it could work in another form, but this form is not it.

Fix: store the recent new game_creation settings in savegames

This allows us to later on see what someone did, and makes sure
that "restart" command still knows how the game was created.

Feature: allow setting a custom terrain type to define highest peak

At least, TGP will try to reach it. It heavily depends on the map
if it is reachable at all. But for sure it will do its atmost to
get there!

Add: allow setting the highest mountain for heightmaps

It will add some slack to the map height limit if that was set
to auto.

Feature: auto-detect map height limit based on generated map

This opens up the true power of the TGP terrain generator, as it
is no longer constrainted by an arbitrary low map height limit,
especially for extreme terrain types.

In other words: on a 1kx1k map with "Alpinist" terrain type, the
map is now really hilly with default settings.

People can still manually limit the map height if they so wish,
and after the terrain generation the limit is stored in the
savegame as if the user set it.

Cheats still allow you to change this value.

Change: rename setting "max_heightlevel" to "map_height_limit"

This better reflects what it is, and hopefully removes a bit of
the confusion people are having what this setting actually does.

Additionally, update the text on the setting to better inform
users what it is doing exactly, so they can make an educated
decision on how to change it.

Next commit will introduce an "auto" value, which should be the
new default. The rename has as added benefit that everyone will
start out on the "auto" value.

Feature: setting to indicate desert coverage for tropic climate

This is an indication value; the game tries to get as close as it
can, but due to the complex tropic rules, that is unlikely to be
exact.

In the end, it picks a height-level to base the desert/tropic
line on. This is strictly seen not needed, as we can convert any
tile to either. But it is the simplest way to get started with
this without redoing all related functions.

Feature: setting to indicate snow coverage for arctic climate (replaces snow line height)

Setting the snow coverage (in % of the map) makes a lot more sense
to the human, while still allowing the niche player to set (by
finding the correct %) a snow line height they like. This makes for
easier defaults, as it decoupled terrain height from amount of snow.

Maps can never be 100% snow, as we do not have sprites for coastal
tiles.

Internally, this calculates the best snow line height to approach
this coverage as close as possible.

Codechange: validate that "max" value of settings fit in their storage

This is an easy mistake to make, so protect us against making such
mistakes, by validating it doesn't happen.

Add: settings to limit your fast-forward game speed

By default this setting is set to 2500% normal game speed.

Feature: configurable refresh-rate and change default to 60fps

Most modern games run on 60 fps, and for good reason. This gives
a much smoother experiences.

As some people have monitors that can do 144Hz or even 240Hz, allow
people to configure the refresh rate. Of course, the higher you
set the value, the more time the game spends on drawing pixels
instead of simulating the game, which has an effect on simulation
speed.

The simulation will still always run at 33.33 fps, and is not
influences by this setting.

Codechange: Don't use cpp_offsetof in the save/load code.

Many of the member variables that are used in save/load are inside types
that are not standard layout types. Using pointer arithmetics to determine
addresses of members inside types that are not standard layout is generally
undefined behaviour. If we'd use C++17, it is conditionally supported, which means
each compiler may or may not support it. And even then using it for individual
array elements is syntactically not supported the the standard offsetof function.

Unfortunately, the trickery employed for saving linkgraph settings causes quite some
clutter in the settings ini files.

Change: Remove disable_unsuitable_building setting

This setting is no longer useful, as you can now always build roads,
canals, etc.

Fix 2fd871e2af5: load correct ending-year for old (pre 0.7) savegames

Despite what it looked like, you could never really change the
ending-year (it was always reset to 2050 on start-up). See commit
683b65ee1 for details. As a side-effect, the variable that was
suppose to store the ending-year was just zero, never containing
a real ending-year.

Fix #8050: ending-year of 5000000 allows you to get to year 5000001 and beyond

MAX_YEAR is set to 5000000, but having an ending-year set to the
same meant you could bypass this, and play till the uint32 wrapped.

The game can either show highscore or wrap year, not both. When
you would do both, every year you get the highscore dialog.

By changing the maximum value of ending-year to 4999999 we prevent
this issue.

Feature: Configurable game ending year

Functionally reverts 683b65ee1

Fix: Snowline height interval is now 1, in both World Generation and Settings windows

- Previously, it was 1 in World Gen window, but 5 in Settings window

Fix: Custom sea level default value is now equal to minimum value, not lower

Custom sea level default value was lower than the minimum

Change: Limit memory allocations for each Squirrel instance

This can avoid out-of-memory situations due to single scripts using up the entire address space.
Instead, scripts that go above the maximum are killed.
The maximum is default 1 GB per script, but can be configured by a setting.

Remove: ENABLE_NETWORK switch

This switch has been a pain for years. Often disabling broke
compilation, as no developer compiles OpenTTD without, neither do
any of our official binaries.

Additionaly, it has grown so hugely in our codebase, that it
clearly shows that the current solution was a poor one. 350+
instances of "#ifdef ENABLE_NETWORK" were in the code, of which
only ~30 in the networking code itself. The rest were all around
the code to do the right thing, from GUI to NewGRF.

A more proper solution would be to stub all the functions, and
make sure the rest of the code can simply assume network is
available. This was also partially done, and most variables were
correct if networking was disabled. Despite that, often the #ifdefs
were still used.

With the recent removal of DOS, there is also no platform anymore
which we support where networking isn't working out-of-the-box.

All in all, it is time to remove the ENABLE_NETWORK switch. No
replacement is planned, but if you feel we really need this option,
we welcome any Pull Request which implements this in a way that
doesn't crawl through the code like this diff shows we used to.

Feature: Industries with neutral stations (e.g. Oil Rig) only supply/accept cargo to/from their neutral station. (#7234)

This change is a controlled by a game setting, located under Environment ->
Industries which allows toggling the behaviour. It defaults to enabled.

"Company stations can serve industries with attached neutral stations"

When enabled, industries with attached neutral station (such as Oil Rigs) may
also be served by company-owned stations built nearby. This is the traditional
behaviour.

When disabled, these industries may only be served by their neutral station.
Any nearby company-owned stations won't be able to serve them, nor will the
neutral station serve anything else other than the industry.

Add: Option for population-linear town cargo generation

Introduce a new default algorithm for town cargo generation (passengers and mail), and a game setting to choose between the new and original algorithm.

The original town cargo generation algorithm has the property of the generated amount relating to the square of each building's population, meaning large towns easily produce more cargo than can realistically be transported. The problem is excessive cargo is amplified if playing with cargodist.

The new algorithm introduced instead has a linear relation to the population. The result is that smaller towns will produce slightly more cargo, while the largest towns will produce about a fourth of what they would with the original algorithm.

Existing savegames will use the original algorithm, while new games will default to the new algorithm.

Codechange: Convert saveload numbers to enum values.

(This was mostly achieved with a few in-place regexes)

Add #4115: default company colour setting (#6998)

Works only in single player.

(svn r25508) -Change: split unit localisation choice into a choice per type of unit, and move it to the advanced settings
-Feature [FS#5482]: have tractive effort in imperial (lbf) and metric (kgf) units
-Feature: have weights and volumes in imperial units (short tons, gallons)