The Django administration UI's Change Form is built around an internal

class structure representing fieldsets, field rows, and fields, all

living in django.contrib.admin.helpers. This computes information

necessary for Django's templates, and is not public API.
Since we heavily customize the administration UI, we've been at the

mercy of Django's logic and templates here. With the administration UI

rewrite, we're wanting to become less dependent on their choices, and be

in a position to more easily notice when they make changes under the

hood.
This change introduces our own class structure, which is built on top of

Django's, but makes use of our CSS component classes and provides state

our templates need. Our customizations start at the fieldset level

(requiring a new template tag to generate them from Django's

AdminForm).
Unit tests are added to ensure all the functionality we depend on works

as expected. This will help us quickly check for changes and have a

mechanism to adapt to them when we upgrade Django in the future.

Unit tests pass on Django 1.6 and 1.11.
Tested the Change Form page for all available models.