Add: settings to limit your fast-forward game speed

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

(cherry picked from commit c3dc27e37e)

# Conflicts:
#	src/gfx.cpp
#	src/gfx_func.h
#	src/settings_type.h
#	src/video/cocoa/cocoa_v.mm
#	src/video/video_driver.cpp
#	src/video/win32_v.cpp

src/misc.cpp

@@ -76,7 +76,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 	ClearDesyncMsgLog();
 
 	_pause_mode = PM_UNPAUSED;
-	_fast_forward = 0;
+	_game_speed = 100;
 	_tick_counter = 0;
 	_tick_skip_counter = 0;
 	_cur_tileloop_tile = 1;