Initial implementation, enough to close this ticket:

Hard-code a list of genres in the code (this way, we won't need to wait for a schema change): MBS-8600
Add a separate box duplicating "tag" functionality using this list. Only allow adding genres through this box which are in our hardcoded list, probably with autocomplete. These tags should still be stored as part of the normal tag list, but:
The site UI will show them separately, and
The WS should include a new "genres" section with these tags, but they should also still remain a part of the standard tag list.

Future tasks:
Move the list to the database: MBS-9491
Let people propose new genres (possibly as Jira tickets?). In the meantime, tell them to enter "unofficial" genres into the normal tag box - if they're accepted, they will get "promoted" to genres.