Add destroy methods to Ninja Body, AABB and Circle

The Sprite.destroy() method calls the Body’s destroy() method if a body
exists. If using Ninja physics, destroying a Sprite will not work,
since the destroy method wasn’t implemented in Ninja’s Body.

Also added destroy() methods to Ninja’s AABB and Circle. Tile already
have a destroy() method.
Merge pull request #581 from dreadhorse/destroy

Add destroy methods to Ninja Body, AABB and Circle