Change: base autosaves intervals on real time (instead of game time) (#10655)

There are two fundamental issues with autosave:
- When fast-forwarding, it saves way too often
- When paused, it never saves

Both makes no sense. Autosaves are meant to prevent you from
accidentally losing your work. The emphasis on "your" work.

To solve both issues, the autosave now works on real time. You
can select every 10 / 30 / 60 / 120 minutes, which are similar to
what the setting was in game-months.

When you pause, autosaving will stop. Unless you make any change
to the game; then it will continue to make autosaves, even so
the game is paused. Unpausing / pausing resets this mechanism.

Change: replace per-AI "start_date" with a global "competitors_interval" (#10653)

The per-AI "start_date" is a lot of custom code, and was rarely
used in the way it was meant.

While at it, also ported this part over to the new timer system.

Feature: Separate rail/road and sea/air velocity units, and add knots. (#10594)

This is achieved by packing vehicle type along with the velocity so that
the string system can decode and pick the appropriate unit.

Fix #10362: NewGRF bridges without speed limits.

For bridges, a max speed of 0xFFFF (i.e. no effective limit)
is no longer displayed as a limit in the UI.

A max speed of 0 is also considered unlimited, for similarity to the
roadtype and railtype interface.

Fix #10363: CargoDist setting helptext shouldn't suggest symmetric distribution for diamonds in subtropic (#10364)

* Fix #10363: CargoDist setting helptext shouldn't suggest symmetric distribution for diamonds in subtropic

* Fix: Always capitalize the first word of a sentence, even if a quoted setting name

Feature: Variable GUI scale.

GUI scale is now variable from 100% to 500%, and no longer restricted to
powers-of-2.

Codechange: Use positional parameters in the base language either for all or for no parameters. (#10111)

This should make it less confusing to translators.

Fix: add back 'Spectate' option to company toolbar menu (#9556)

This was removed in ce7406f88b, but people used this to quickly
mark themselves as away.

Co-authored-by: dP <dp@dpointer.org>

Fix: [Network] show query errors in the server listing instead of error popup (#9506)

When you are query several servers at once, it is rather unclear
for which server you got a popup. Instead, show any errors on the
server itself.

This is only true for the query-part. Joining a server still gives
an error popup to tell you about any issue.

Fix #9492: show for what server a relay session is being created (#9494)

Currently it says "the server" which is a bit ambigious. Be more
specific.

Fix: report reuse of invite-code and switch to local game-type (#9487)

This prevents two servers battling for the same invite-code. Now
the last one wins.

Feature: make "join game" button join the game, instead of first showing a lobby window (#9467)

Nobody really paid attention to the lobby window, and it completely
missed its purpose. Most people don't even wait for companies to
show up, but just hit "New Company".
This in turn means people create a lot of unneeded companies, while
they "just want to watch the game" or join another company.

Instead, "Join Game" now just joins the game as spectators.

Fix: name the Online Players caption the same as in the menu (#9473)

Referring to one window in two ways is a bit annoying.

Change: remove the ability to control "max spectators" (#9466)

Soon we will make "join game" join the game as spectator first,
so limiting the amount of spectators makes no sense anymore in
that context. Not sure it ever did make sense.

Feature: allow the use of TURN to connect client and server together

TURN is a last resort, used only if all other methods failed.
TURN is a relay approach to connect client and server together, where
openttd.org (by default) is the middleman.

It is very unlikely either the client or server cannot connect to
the STUN server, as they are both already connected to the Game
Coordinator. But in the odd case it does fail, estabilishing the
connection fails without any further possibility to recover.

Feature: allow the use of STUN to connect client and server together

This method doesn't require port-forwarding to be used, and works for
most common NAT routers in home setups. But, for sure it doesn't work
for all setups, and not everyone will be able to use this.

Add: inform clients what game-script a server is running (#9441)

Co-authored-by: The Dude <thedude@novapolis.net>

Add: allow setting your server visibility to "invite-only" (#9434)

In this mode you do register to the Game Coordinator, but your
server will not show up in the public server listing. You can give
your friends the invite code of the server with which they can
join.

Feature: join servers based on their invite code

This removes the need to know a server IP to join it. Invite codes
are small (~7 characters) indentifiers for servers, which can be
exchanged with other players to join the servers.