For some reason (probably because it felt like overkill) we originally implemented the genre_alias table without support for alias types. That seems problematic though, because there's at least the usual case of "typo" and "name in a specific language", so "search hint" vs "genre name".

This involves adding a new genre_alias_type table mirroring other entities, and also altering the genre_alias table to add a type column. Since the genre_alias table is unused in production, this won't affect mirror servers. It should only affect standalone servers if they have for some reason used genre_alias locally. While we're doing this, we will also update genre_alias to have other alias fields that were ignored at first (sortname, dates). Any local data will be kept in the new format, and set to type "Genre name".