The new revised administration UI templates left out some crucial blocks

that were necessary for some extensions to work, and broke the ability

to override the form submission buttons.
This was largely due to an attempt to simplify the templates, removing

some Djangoisms that didn't appear to make sense, and to also utilize

some other Djangoisms for calculating state needed for form buttons.

What we had just wasn't comprehensive enough.
What we're doing now is bringing back some of the blocks, fixing up some

bad assumptions with the buttons (and allowing them to be better

overridden), and also fixing some incorrect usage of some CSS components.
There's also fixes to the form that previously caused dependencies on an

adminform variable. Most of these are fixed in this change, with a fix

to media coming in a follow-up change.
There's room for improvement here, particularly when it comes to the

form buttons. Eventually we'll want to move away from Django's

{% submit_row %} template tag (which breaks if not working with

models), but that's a task for another day.

Tested the model change pages, settings pages, and the Power Pack

configuration page (which was broken before). They all now render as

expected.