Remove: DOS support

In 10 years there was no active development on DOS. Although it
turned out to still work, the FPS was very bad. There is little
interest in the current community to look into this.

Further more, we like to switch to c++11 functions for threads,
which are not implemented by DJGPP, the only current compiler
for DOS.

Additionally, DOS is the only platform which does not support
networking. It is the reason we have tons of #ifdefs to support
disabling networking.

By removing DOS support, we can both use c++11 functions for threads,
and remove all the code related to disabling network. Sadly, this
means we have to see DOS go.

Of course, if you feel up for the task, simply revert this commit,
and implement stub c++11 functions for threads and stub functions
for networking. We are more than happy to accept such Pull Request.

Fix e66cec8f86: Permit loading of industry production callback with invalid cargo type.

It is only an error if the invalid result is actually used. This will be silently ignored at the moment.
It is still an error if a duplicate cargo type is returned.

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.

Remove: BeOS support (deprecated by Haiku)

In 10 years there is no commit to change how BeOS works, and we
have no active maintainer for it. It is unlikely it works in its
current state (but not impossible).

With the arrival of SDL2 (and removal of SDL), BeOS is no longer
support. SDL2 suggests to use Haiku instead of BeOS.

Remove: MorphOS / AmigaOS support

In 10 years there is no commit to change how MorphOS works, and we
have no active maintainer for it. It is unlikely it works in its
current state (but not impossible).

With the arrival of SDL2 (and removal of SDL), MorphOS is no longer
support. There is an SDL2 port for MorphOS, but it is not maintained
by upstream SDL2, and nobody can currently test it out.

If anyone wants to re-add MorphOS, please do (revert this patch,
fix the problems, and create a Pull Request). If you need any help
doing so, let us know! It is not that we don't like MorphOS, it is
that we don't have anyone fixing the problems :(

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.

Feature: Add option to adjust font size separately from GUI size. (#7003)

Adds an option in the "Game Options" next to "Interface Size" called "Font Size". Available options are normal, double, and quad.

Feature: Group liveries, and livery window usability enhancements. (#7108)

* Change: Replace checkbox in livery selection window with Default option in drop down selection.

This reduces clutter in the UI and allows for primary/secondary colours to independently follow the default scheme if desired.

* Feature: Add vehicle group liveries.

Fix 8859381: Display of requires/produces in Build Industry window

Change the window to use a dynamically generated string of cargoes,
instead of one of a few fixed-length lists. With up to 16 cargoes
on each list, having 16 with the only difference how many are listed
seems like a bad maintenance idea.

Add: Mexican Peso currency

OpenTTD doesn't have any pesos, so I've added Mexican pesos,
at its current exchange rate: 1GBP = 24.39MXN, rounded to 24.

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

Works only in single player.

Add: Filter box to the save and load windows (#6974)

Save and heightmap names can be filtered.

Feature: Framerate display window (#6822)

Frame rate and various game loop/graphics timing measurements and graphs. Accessible via the Help menu, and can print some stats in the console via the fps command.

Add: Hover tool-tips to cargo dest flow legend window.

This is to improve the usability of the window.
The two-letter abbreviations are not always clear, in particular
when using a large number of cargoes.
The company colours can be ambiguous when there are a large
number of companies.

Change: Use name of cargo instead of Passengers/Mail in town statistics. (#6801)

* Change: Use name of cargo instead of Passengers/Mail in town statistics.
* Cleanup: Remove strings from all language files.

(svn r27751) -Feature: Display cargo suffix of accepted cargoes in industry view based on cb37 result type.

Industry-sets that have no stockpiling get better control over the displayed accepted cargo information.
- result 0401 only prints the accepted cargo
- results 0800-0BFF prints the accepted cargo and a string (but not the amount)

(svn r26733) -Fix [FS#6086]: inconsistency in using spaces between number and unit in some strings
Try to follow the SI recommendation to use a non-breaking space between a number and its units (and prefix)