added MoveableObject class which Player and Enemy inherit from
overloaded Enemy::chase to accept any MoveableObject
removed checkIfOnTile in MoveableObject class since it is only for the Player object
- fixed a bug where restarting the game wouldn't reset the number of
  currently flipped tiles.
- the game now properly resets when pressing the 'r' key, even after
  dying.
- the checkIfOnTile is now done in QMan.pde and not in
  MoveableObject.pde