TiledLevel lighting, few minor changes

Tiled levels do now have lighting!
The light value for each tile is calculated by checking the surrounding
tiles. The amount of emitted light can be changed for each tile by
overriding the function "getLight()".

There were a few other changes, too:
* The ScreenLoading is now more useful since it is actually displayable
while the game is still loading.
* The sound system doesn't have any console output anymore.
* The "keys" array in class Keyboard does now have a length of 65536
instead of KeyEvent.KEY_LAST since it was found to be unreliable.