Test against wtforms2
Create Meta in a WTForms2-compatible way

Allow each class Meta to be a subclass of its base class' metas. This
allows changes to the base classes to propagate via normal inheritance
logic, also the Meta isinstance of all the other metas.
Merge branch 'wtforms2-support' of https://github.com/crast/wtforms-alchemy-work into crast-wtforms2-support

Conflicts:
	tests/test_configuration.py
	wtforms_alchemy/__init__.py