Remove mandatory dependency from CMFCore

If transmogrifier is so great, why not to make it work also outside CMF context?

This pull removes CMFCore dependency so that transmogrifier could be installed without CMF/Plone KGS.

I'm working the next week with a non-Plone (actually, non-Python) migration project, where migration pipeline should from Transmogrifier should be useful.

I'll probably add also some kind of command-line hook/script, which accepts a Python class path as context factory and another argument as executed pipeline. Any other ideas? Should I make all thinks as separate pull requests (event when they all are based on top of another)?