Changing visibility of subclasses and statistics functionality.
Renaming 'CompactNode' to 'CompactMapNode'.
Renaming 'AbstractNode' to 'AbstractMapNode'.
Renaming specialized classes.
Renaming inner static interfaces.
Using the same code generator for specialized set/map nodes. Made their codebases more equal.
Fixing deletion behaviour to keep Trie consistent.

Also fixed a copy and paste bug in PDBPersistentHashSet.