This is good when having lots of re-used shapes with different sizes.
Convex shapes will need to derive from btConvexInternalShape (which is a subclass of btConvexShape). We could have renamed btConvexShape to 'btConvexShapeInterface' (can still do that later)
CompoundShapes are tricky to manage with respect to persistent contact points and swapped order of btCollisionObjects,
During dispatch, finding an algorith etc. order can be swapped.
fixed several other issues, related to SimpleBroadphase (removing a proxy was not working)
