Consistently use angle brackets for SDL.h includes

That's how it should be done, because the SDL headers aren't going to be
installed in this repository. The game was a bit inconsistent before but
now it isn't anymore.

desktop_version/src/Game.h

@@ -3,7 +3,7 @@
 
 #include <vector>
 #include <string>
-#include "SDL.h"
+#include <SDL.h>
 #include "Maths.h"
 #include "UtilityClass.h"
 #include "GraphicsUtil.h"