The config forms code wasn't allowing errors to be shown on the forms,

and had other issues that prevented proper error reporting:
1. We didn't implement a post() function on the view, meaning that

   TemplateView would default to a Method Not Allowed.
2. We weren't replacing the form instance within the page, resulting in

   a clean form being used, free of errors.
3. We weren't showing non-field errors on the form.
This fixes these cases so that form validation errors will be shown

correctly.
It also moves all the POST handling into the new post() function, where

it really belongs.

Successfully saved new form data.
Failed to fill out a required field, and saw the proper validation error.