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.

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: "???"