One of the big inspirations for designing a new component library was

the mishmash of layout and styles that is the Config Forms suite of

components. This was an early attempt at standardizing the presentation

of forms, collections of forms, and fields, and we've learned a lot from

this. In time, the hope is to deprecate the vast majority of this module

in favor of Ink.
For now, we need to style this using Ink. This change begins that

process, moving much of the styling to Ink, and fixing up some small

layout issues in the process. This gets us dark mode and some

consistency in presentation.
We're also using ink-c-button now for action buttons in lists and

submit buttons in forms, and ink-c-spinner instead of

djblets-o-spinner.
Some related usage in the codebase (namely avatar forms) have been

updated as well.
This looks much as it did before on light mode, though we're making more

use of the accent color for selected navigation items. Dark mode looks

about as expected.
The Config Forms consumers often specialize much of the styling of

Config Forms, so changes will still be needed there.

Unit tests pass.
Tested all of the My Account page on light and dark mode, with all

options available on all pages. There are still issues to address, but

they'll require further work in Review Board and in other modules in

Djblets.