Update the Djblets 1.x code reference docs and add links to guides.
Review Request #10827 — Created Jan. 17, 2020 and submitted
This adds a few missing modules to the code reference docs, helping cover
more of the codebase. This includes the fallback avatar backend and some
Django compatibility modules.
It also adds "See Also" links for several of the modules, pointing to
Built the docs. Checked for broken links.