Call static methods via classes where they are actually defined
Removed stdlib type cache unused after the switch to python-skeletons
Removed unused PyBuiltinCache.isValid()
Rearranged fields and constructors
Fixed PIEAE in referencing obsolete cached PSI elements for built-in 'str | unicode' type

There was no significant performance boost, so the cache has been simply removed.
Merge branch 'pieae-in-python-builtins-cache'
REGISTERED state added