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.

Display Condition type in list views

* Whether a Flag is disable-if-false or enable-if-true is a very
important detail
* But one that's easy to get wrong
* And it's hard to spot problems without inspecting every single flag

This change adds the Condition into the various admin list views, so
that it's easier to scan them all for problems and look for inconsistencies.

git subrepo pull vendor/registrasion

subrepo:
subdir: "vendor/registrasion"
merged: "c1e194a"
upstream:
origin: "git@gitlab.com:tchaypo/registrasion.git"
branch: "lca2018"
commit: "c1e194a"
git-subrepo:
version: "0.3.1"
origin: "???"
commit: "???"