This backports parts of zope commit bb7837c66 (Explicitly make all
classes new-style., 2017-09-15) and 173658008 (Fix unpickling of instances
those base class changed to a new-style class. (#208), 2017-10-24).

This is done for two reasons:
 - so that business template XML are same when exported from zope4
   and from zope2
 - so that a business template created from zope4 can still be
   installed on zope2.