While the ADR #2445 (related to #1622) is finalized, reviewed, approved, and implemented it would be great to have at least:

• change SignBytes to use amino encoding
• add an error message to the types registered in socket.go (as requested by @xla)

For the latter, I would still split up SignVoteMsg into SignVoteRequest and SignedVoteReply. Only SignedVoteReply will contain a potenial error. The original types (e.g.Vote) will remain unchanged.

This would unblock a MVP kms that signs Votes, Proposals, and Hearbeats (see related wip PR: tendermint/tmkms#55). Also, independent from how the exact structs will look like, we will switch to amino (instead of JSON). This would be a rather incremental, smaller change into this direction.