Revamped the collision handling and PhysicsComponent instantiation code

-Added 2 new Entity callbacks: Enter and Leave
 +These trigger when an entity starts/stops colliding with another
  entity
-Adding PhysicsComponents should be much easier now
 +New syntax(for now) is:game.addComponent(id, 2, position.x,
  position.y, position.z, rot.x, rot.y, rot.z, rot.w, collision
  shape, shape arguments(varies by shape), (optional)mass)
 +This removes some features, but they will be added back soon. I have
  some other things that I want to sort out before I continue, and in
  the short term this is still an improvement.