Allow Featured Artist tracks to be assigned multiple genres

[Ephemeralis]

As our library grows, searching it meaningfully becomes a considerably harder feat. Efforts to address this by more in-depth genre assignment are stifled by one key fact: genres are currently a one-to-one field on FA tracks when their actual usage should be one-to-many.

Multiple genres associated with one track allows for more granular searching. It would be ideal to have this before we proceed with organizing a team to categorize all 6300~ tracks, to avoid having to do this again in the future.