Make fixes for deprecations in Django 3.2 and Python
- Add new "DEFAULT_AUTO_FIELD" Django 3.2 setting
- Fix deprecated (in "gettext") use of non-int numbers for selecting
plural translations
- Provide "get_response" callable when creating middleware-factory
instance in tests
The idea of splitting integration from unittests is good in theory
but leads to a lot of mental overhead. Besides whenever a tests
interacts with a database it isn't a unittest anyway.