Update to Django 2.2

Upgrade site and modules to Django 2.2. Remove and replace obsolete
functionality with current equivalents. Update requirements to latest
versions where possible. Remove unused dependencies.

Remove wagtail

This should eradicate wagtail from the project.

While wagtail may be nice, our goals are to keep all things public, and
having things locked behidn a DB is congruent to that plan.

All in all, the django project only leveraged a single wagtail feature,
"richtext" which has been hacikly removed and will result in bad display
of however it comes up. But this is on homepage.html, which will be
removed and covered up with a static website, which means we should be
able remove homepage entirely from this project.

This reduction hopefully makes the monolith easier to understand,
maintain, and wield.

Remove boxes

Boxes takes content directly from the DB and drops it into the django
templates. This is rather ugly and goes against keeping as much as we
can in static locations. As such, this is being dropped.

Added some css to make text visible on 404 and 404 pages.
Removed references to non-existent content—page-header-panel.html.

Customises the CSRF failure view so that it uses the LCA2017 style (#53)

* Customises the CSRF failure view so that it uses the LCA2017 style

* If a user is logged in and there is a bad_token failure, let them know.