Upgrade to Django 2.2.28

[willgearty]

Once we have upgraded to python3, we will finally be able to upgrade Django. The first step of that involves upgrading from 1.11.29 to 2.2.28. We'll need to do the following:

• fix all the warnings we can find in logs (@milescalabresi can you please do the same grepping that you did for the last upgrade?)
• read the changelogs (https://docs.djangoproject.com/en/5.1/releases/)
• upgrade to Django 2.0.13 (https://docs.djangoproject.com/en/5.1/releases/2.0/)
• upgrade to Django 2.1.15 (https://docs.djangoproject.com/en/5.1/releases/2.1/)
• upgrade to Django 2.2.28 (https://docs.djangoproject.com/en/5.1/releases/2.2/)
• address deprecated features of Django 2.2.28 (https://docs.djangoproject.com/en/2.2/internals/deprecation/)
• upgrade dependencies as needed
• do some testing (looking at you, @kkbrum)