Remove sprite and drawable fields from the Entity class.

These were not being used.
Refactor PlayerInputProcessor to be PlayerInputHandler.

The PlayerInputProcessor class was renamed to PlayerInputHandler. And, instead of implementing InputProcessor directly, it now extends InputAdapter; which simplifies the handler class.

Also, the getTouchUp method is now hasTouch.
Move assets directory to the android project, and add IntelliJ IDEA support.

The assets directory had to be moved to allow the projects to be built in IntelliJ IDEA.
Update libGDX to nightly-20130322.
Implement gravity manager.

Close #6