Added AABB::, OBB::, Frustum::ToPBVolume() member functions and removed the old global ToPBVolume(Frustum) member function.
Add a new unit test for computing the center of mass for the set intersection of two OBBs. Fixed functions Polyhedron PBVolume::ToPolyhedron(), Polyhedron::ConvexCentroid() and Polyhedron::Contains when the Polyhedron is degenerate.