Added before_all_insert/after_all_insert methods

which also fire when adding a new model via REST or Formalchemy
Fixed record insertion via admin
formalchemy: only pass the session in when analyzing a class
Cleanup the before_insert/after_insert stuff.

before/after_insert is now called from my own _flush() method
and not via some sort of signal, because the signal runs within
sqlalchemy's unit of work and thus cannot add new objects.
removed obsolete and skipped test
removed broken import