The Django newforms-admin and full newforms migrations happened in trunk recently, so we needed to update accordingly.

This change strips out all the inner Admin classes from the models and moves to the new Admin classes in admin.py files. We auto-discover early on (making sure we only do it once so that we don't break unit tests -- will need to ask Django to fix this in the future). We also move to importing django.forms instead of django.newforms.

Ran all unit tests and made sure the admin site was working as expected.