Leverage MusicBrainz and Discogs performer credits from db downloads into track level metadata

[audiomuze]

Incorporate MusicBrainz and Discogs DB's as metadata enrichment sources for contributor metadata.

[audiomuze]

MusicBrainz track and performer metadata emitted from mbdump. Ingestion to be tackled when work and performance identification is improved. Strictly speaking users should use a tagger like SongKong for this, calling into question the need to do this in tm given SongKong pulls MusicBrainz and Discogs metadata.