Moved camera logic out to a trait
Camera now stops at all level boundaries

Be warned, however: if the level boundaries are small enough, the camera will
bug out slightly and allow the player to see beyond (0,0). Please see the size
of LevelOne for (almost) the smallest size you can make a level horizontally.
Changed brick texture to square box texture
Merge branch 'vineet/graphics' of https://github.com/Freezerburn/cmsc425-loderunner
Added detection for player jumping into the abyss