Adding enum to TBranchElement to clarify Type numbers

(cherry picked from commit caec9c2a21b520cd456041b77fcda0b52d8ab286)

Conflicts:
	tree/treeplayer/src/TTreeReaderValue.cxx
Added method to get the size of the class

(cherry picked from commit beafe941588df210e50d209fc951bcace6181a1f)
Fix TClass::GetClassSize() to also work for CollectionProxy case: use Size().

(cherry picked from commit 6fecd500190c9f08edd6f2e03c5cf5ec8770d707)