Integration test scripts for user registration

Addresses #786
Fix import error related to django-social-auth

The exception classes seem to have gotten moved between different
versions of django-social-auth.  Add a try/except around the import
to support the different locations.
Support django-registration 1.0

With version 1.0, django-registration switches to using class-based
views rather than function-based views and backend classes. This
commit updates our registration customizations to work with
class-based views.

Addresses #786