Djblets 2.0 got a major update to config forms, moving to our modern CSS

component model and fixing up a bunch of styling. Everything in Djblets

was updated to use this except, ironically, the module that introduced

config forms in the first place.
The actual configforms Python module and related JavaScript code is

responsible for pages like the My Account page in Review Board, or the

admin UI in RBCommons. This module was still using legacy naming, which

meant we weren't able to get some of the benefits of newer styling, and

were building UIs that needed workarounds for layout.
This change moves this last remaining part of Djblets to the modern

components.

Unit tests pass.
Tested each page in My Account