The config forms CSS styles were hobbled together from a bunch of styles

found in Review Board, RBCommons, and Splat, and in the process of

moving these into Djblets, we ended up with some unwanted rules and some

very specific styling and naming that didn't make sense to keep in

Djblets. We also have some new styles coming for config forms that was

hard to put in without a bit of a cleanup.
This change moves the styles to our new CSS naming standards, helping

create a more logical, organized, documented set of components we can

build upon, and in the process helps us move away from a bunch of

unwanted styles. We still have those styles, and the old names, for

backwards-compatibility purposes, but going forward we have a stronger

foundation to build upon, and a clear path to deprecation.
Some of these styles might come back in some other form later, but the

intent is to go back to something closer to a bare minimum. That said,

none of this is set in stone yet, and there are many form-related styles

that deserve its own cleanup (and are not considered "stable" at this

point).

Tested that all the backwards-compatibility parts work with the My Account

page in Review Board and both the My Account and Team Admin pages in

RBCommons.
Made use of some of the new styles in some upcoming work.