When segwit address is used to sign, we need to return the address signed with.

[DennisAMenace]

This is a follow up to PR #66 where I said:

Is there a way we can sign with the Bech32 address and not the underlying base58 address?

If there is not a better way, I would suggest that the base58 address is returned with the signature string.

This is the PR for that suggestion as that PR was committed without any further input, so this will provide a solution until a better solution is presented.