Refactor MainGamePanel to GameEngine

This is where the main set up stuff should go.  ie. all of the model,
view, and controller initializations.  This also holds the main update
and render functions.
Remove unused classes
Refactor everything to be more MVC friendly

A few things are still incomplete, such as AnimatedSprite.  Right now,
AnimatedSprite still holds a render/draw function which it should not.