Old versions of Django used django.core.urlresolvers as the module for

most URL-related imports. That's since been changed to live in

django.urls. Along with this, some of the names have changed (all

Regex prefixes were dropped, for instance).
This change updates all of our imports to use the new imports and names.

This is compatible with both Django 1.11 and 3.2.

Unit tests pass on Django 1.11 and on 3.2 (along with other in-development

changes).