Refactor CSS to use standard Tailwind-style utility classes instead of
ad-hoc rules. This eliminates a lot of single-purpose rules for specific
UI elements and standardizes margins to be more consistent throughout
the site.
Utility classes are defined manually on an as-needed basis instead of
importing Tailwind as a whole. Naming conventions mostly follow
Tailwind's conventions, otherwise they follow Bootstrap.
* https://tailwindcss.com/docs/
* https://getbootstrap.com/docs/5.0/utilities/spacing/
- "Current" is now most like the old format
-- It is therefore now the default for post versions
- Only show the actual edits in their own column
- Show the current state at that version in another column
- On the "previous" view, don't double-show full list of tags for
the first post versions, so leave edits blank
* Add search form above table.
* Move thumbnail to left of table when viewing history of single post.
* Remove unrelated links from subnav menu.
* Fix bugs with changed_tags search.
