bug#41300: Upgrade to Django 3

[Josh Marshall]

Here's to track work for getting django 3 ready

Requires:

python-wrapper <insecure>

bash <present>
python-bcrypt <present>
python-docutils <present>
python-numpy <present>
python-pylibmc <present>
python-memcached <present>
python-PyYAML <present>
python-tblib <present>


gettext <out-of-date>
python-argon2-cffi <out-of-date>
python-geoip2 <out-of-date>
python-Jinja2 <out-of-date>
python-Pillow <out-of-date>
python-pytz <out-of-date>
python-setuptools <out-of-date>
python-sqlparse <out of-date>
python-flake8 <out of date>
python-tox <out of date>
python-isort <out of date>


python-pipdeptree <missing>
python-asgiref <missing>
python-selenium <missing, optional>
  - selenium <missing>
python-pywatchman <missing>