Physics fixes.

* Restore body rotation interpolation
* Spout interpolation is only on non-bodies
* Minor PhysicsComponent cleanup
* No longer add bodies on spawn (region is valid in onAttached)
* No longer perform callbacks if an entity was removed prior. This may end
  up changing as one plugin could virtually "block" callbacks to other
  plugins. Education may be needed here to check for removed statuses.

Signed-off-by: Chris Sanders <zidane@outlook.com>