Add being able to toggle over/fixed-30-FPS, off by default

There is now an option in "graphic options" named "toggle fps", which
toggles whether the game visually runs at 1000/34 FPS or over 1000/34
FPS. It is off by default.

I've had to put the entire game loop in yet another set of braces, I'll
indent it next commit.

desktop_version/src/Game.h

@@ -401,6 +401,8 @@ public:
     {
         return inintermission || insecretlab || intimetrial || nodeathmode;
     }
+
+    bool over30mode;
 };
 
 extern Game game;