Avoid cloning volumes more than once for the same node in alignment (saves...

Avoid cloning volumes more than once for the same node in alignment (saves memory). Added reference counting for volumes - for now just counting how many instances the volume has in nodes. Fixed node bits which were overwriting TObject bits space. Do not allow setting max threads if geometry not closed. Removed assigning dummy media to assemblies. Improved debugging info for assemblies.
(cherry picked from commit c2802738)

Conflicts:

	geom/geom/src/TGeoPhysicalNode.cxx