Cleanup and bbb removal

Reduced dependencies and declared them explicit.
Do not directly depend on ``Products.CMFPlone`` any more.
Pep8fied et al.
ATCT is now an extra require.
Skip Zope2 old style interfaces.
Stop Plone 3 support in 1.1 series (remove bbb+patches).
Get rid of old outdated interface fallbacks.
I don't see any references (quick git grep I must admit) to plone.app.testing, but it does indeed need to be ported to plone.app.testing: https://github.com/plone/Products.CMFPlone/issues/306