PubLookup.lookup to return an array of public keys

[tomholub]

after #553

we are blindly choosing .first public key which is not ideal, and instead in the future we should return [Contact]. If we are pulling keys during compose to save them in db, save all of them

Originally posted by @tomholub in #296 (comment)

[tomholub]

This is important for future work on key lifecycle functionality (rotation, expiration / extension, revocation)