Add support for OnObjectEnter, OnEnterObject, OnObjectLeave and OnLeaveObject events.

These events are not yet ever called. This will be coming in the next commits.
Scene will now post OnObjectEnter, OnEnterObject, OnObjectLeave and OnLeaveObject events.

There are still a few bugs to iron out, but the main functionality is there.
Fix a bug where the scale of newly added child shapes were not being set correctly in CollisionShapeComponent.