We have several templates throughout Review Board and Djblets that

define the structure of a form. This is partly because we used to not

have a standard. The closest thing was how the Django admin UI defined

forms, which was heavily model-centric in places.
In an effort to standardize how forms were used, and to allow Djblets

components to work in both standard forms and the administration UI, we

introduced a series of templates in Djblets that defined the

presentation of forms and non-model-based administration change pages.

In retrospect, the approach used there wasn't as future-proof as we

liked, but that's a problem for another day.
This change defines a new set of templates under templates/forms/ for

how a fieldset and a field look, making use of our CSS component

classes. These are effectively ports of the Djblets form templates,

updated to use our classes.
We provide overrides for some of the Djblets templates that forward on

to these templates, along with some additional templates that override

how to interface with our new administration UI.
This isn't the final iteration of this. An effort is planned to bridge

the new admin templates (which are still separate) and the new ones, but

before that some work is planned for Djblets to create a new set of

renderer classes for forms that will give consuming projects full

control of template rendering, removing the need in the future to handle

all these specialized form templates.
For now, this change is enough to provide a proper UI for most of the

remaining pages in the administration UI, particularly (most of the)

settings pages.

Tested a few pages that make use of the Djblets templates. Verified that

we were now using our CSS component classes for forms.