Single tag index page and multi-AV file support

[camdendotlol]

Summary

This PR builds on #59 by adding the remaining features from Figma:

• single tag page
• support for multiple audiovisual files and multiple sets
• updates the tag display code to use cleaner URLs (e.g. /My Category/ to /my_category/)
• refactors this param logic to use some standardized heplper functions in @utils/tags
• fixes a bug in the tag category page where a band wouldn't be the correct color if the first tag in its list of tags wasn't part of that category

Screenshots

Multiple AV files

(I named my test files things like "AV File 1" and "AV File 2" - I don't think there's any relevance to the sort order)