add showCursor() and hideCursor() functions to MOAISim

When developing something game-like on a PC system, it is usually necessary to disable the system cursor. I've added MOAISim.showCursor() and MOAISim.hideCursor() functions so that this would be possible. Just so you know, they are copy-pasted versions of EnterFullscreen and ExitFullscreen, This change also affects the GLUT host which sets the AKU* callbacks.

Please check it out!