Select3D_SensitiveSet now stores BVH_PrimitiveSet as class field (no dynamic allocation),
and BVH_PrimitiveSet subclass now stores raw pointer to Select3D_SensitiveSet (no smart pointer).
Select3D_BVHPrimitiveContent definition has been moved into Select3D_SensitiveSet
class definition to avoid confusion.
Unused field Select3D_SensitiveSet::myIsLeftChildQueuedFirst has been removed.