Add signmessage / signmessagewithname

[pinheadmz]

See https://blog.ledger.com/btchip-doc/bitcoin-technical-beta.html#_sign_message

and https://github.com/LedgerHQ/app-bitcoin/blob/master/src/btchip_apdu_sign_message.c

Would be great to get this into the ledger app now that signmessageiwthname is merged into hsd and bob wallet.

[CorpulentBrony]

This would be especially helpful since some sites that use HNS for authentication require you to sign a message. This is impossible to do today using Ledger.