Add: draw the screen at a steady pace, also during fast-forward

During fast-forward, the game was drawing as fast as it could. This
means that the fast-forward was limited also by how fast we could
draw, something that people in general don't expect.

To give an extreme case, if you are fully zoomed out on a busy
map, fast-forward would be mostly limited because of the time it
takes to draw the screen.

By decoupling the draw-tick and game-tick, we can keep the pace
of the draw-tick the same while speeding up the game-tick. To use
the extreme case as example again, if you are fully zoomed out
now, the screen only redraws 33.33 times per second, fast-forwarding
or not. This means fast-forward is much more likely to go at the
same speed, no matter what you are looking at.

src/openttd.cpp

@@ -1465,7 +1465,6 @@ void GameLoop()
 	if (_game_mode == GM_BOOTSTRAP) {
 		/* Check for UDP stuff */
 		if (_network_available) NetworkBackgroundLoop();
-		InputLoop();
 		return;
 	}
 
@@ -1505,8 +1504,6 @@ void GameLoop()
 
 	if (!_pause_mode && HasBit(_display_opt, DO_FULL_ANIMATION)) DoPaletteAnimations();
 
-	InputLoop();
-
 	SoundDriver::GetInstance()->MainLoop();
 	MusicLoop();
 }