Fixed and Updated GameController

There were some problems in GameController which had been bothering me,
so those have been fixed. I also added the ability to render background
images as well as added animation functionality and the ability to
change sprites for an object.

I tried to get this to work with PhysicsObject's boundingBox, but I am
not quite sure how it works, and I could not get a hold of Tim. If Tim
sees a problem, have him contact me and we can sort out the issues.