We now show a list of users and allow you to deactivate a user using the
same process as `python manage.py deactivate_user`.
We add a new menu item accessible from the gear icon which will eventually
have much more than just this, but we have a good start here.
Here we also add a property to UserProfile which determines whether you're
eligible to access the administration panel, and then have code which shows
the menu option if so.
This introduces a new JS file, admin.js.
(imported from commit 52296fdedb46b4f32d541df43022ffccfb277297)