Tag.category_for looked up a tag's category in the Redis cache. This was
only used in a few places (in related tags, and on the popular/missed
search pages). Get rid of this method so we can work towards getting rid
of caching tag categories in Redis.
Revert back to previous workaround of fetching previous day if current
day returns no result. A terrible hack, really we should convert dates
to Reportbooru's timezone, but that has other complications.
* Combine MissedSearchService, PostViewCountService, and
PopularSearchService into single ReportbooruService class.
* Use Danbooru::Http for these services instead of HTTParty.
* Replace the .category-N CSS classes on tags with .tag-type-N. Before
we were inconsistent about whether tag colors were indicated with
.category-N or .tag-type-N. Now it's always .tag-type-N.
* Fix various places to not use Tag.category_for. Tag.category_for does
one Redis call per tag lookup, which leads to N Redis calls on many
pages. This was inefficient because usually we either already had the
tags from the database, or we could fetch them easily.
