Make Entity a subclass of Box2DBody for propery physics integration.  Note they will only have physics if they are a child of a Box2DWorld.  Scene now iterates children of Box2DWorld looking for entities for updates.
Updated ref for qml-box2d submodule
Updated qml-box2d submodule to fix a potential crasher in angularVelocity
Merge pull request #11 from kenvandine/box2d-entity

Make Entity behave by inheriting from Box2DBody