Add django-registration-redux app

This required renaming our "registration" app, to avoid conflicting app
names.

Since only the login views were left once Django Registration views were
removed, I decided to name the app "login"
Add basic templates.

The registration templates were taken from Django Registration Redux's
sample templates.
Remove Django Sites framework.

django-registration-redux and auth.contrib will use the domain name
from the request, which works well enough and is also better for
development.
Change collected static directory to a more obvious name
Remove lint
Use unique email address form for signup.

Also:
Split login/urls.py into a package and move registration urls there.
Fix running the test suite through manage.sh

Apparently the DiscoverRunner needs to be run from the project directory.

Since the Django docs generally show manage.py being used from the
directory it is in, I just changed manage.sh to always run from /opt/app
Use core.User for the auth user model.

Unique email addresses are verified in a full clean method, instead of
with `unique=True` so that we can subclass AbstractUser instead of
AbstractBaseUser.

Also adds `blank=True` to `requested_individual_mapping_at` to allow null
values to pass `full_clean`
Switch to filebased email backend for development
Remove references to site.name