for tokens with editions, track.erc721.tokenId, track.erc721.tokenURI may not make sense

[TimDaub]

• say we have a track that is represented by e.g. 5 editions, when it could be that those are all at a different tokenId and that the tokenURI points to a different uri every time
• in that case, the current schema doesn't really make sense as those values should e.g. be a list of tokens