acoustid: Add support for creation_date
According to Picard website (https://picard.musicbrainz.org/docs/mappings/), the creation date is the earliest release in the release group.
Acoustid test is also updated to retrieve the creation_date.
According to Picard website (https://picard.musicbrainz.org/docs/mappings/), the creation date is the earliest release in the release group.
Acoustid test is also updated to retrieve the creation_date.