Fix category prefix metatags not working in autocomplete. Now typing
e.g. `copy:t` will show tags starting with 't' in autocomplete.
Also fix it so that tags beginning with a '(' work in autocomplete.
Typing e.g. `-(tou` will show `touhou` in autocomplete.
This also fixes it so that when you type a negated tag in autocomplete,
e.g. `-touhou`, it sends `touhou` in the autocomplete API call, rather
than `-touhou`. This makes caching more effective since negated tags
will be cached the same as non-negated tags.
Restructure the Dockerfile and the CSS/JS files so that we only rebuild
the CSS and JS when they change, not on every commit.
Before it took several minutes to rebuild the Docker image after every
commit, even when the JS/CSS files didn't change. This also made pulling
images slower.
This requires refactoring the CSS and JS to not use embedded Ruby (ERB)
templates, since this made the CSS and JS dependent on the Ruby
codebase, which is why we had to rebuild the assets after every Ruby
change.
