Mirror the public Nunchuk Tapsigner interface in Flutter

[PeteClubSeven]

NFC functions, these need to be ran within TapProtocolThread:

• Tapsigner::Tapsigner(transport) - Could add this to avoid requesting status twice when we expect a Tapsigner
• Tapsigner::Derive(path, cvc) - Return the response as a Dart struct
• Tapsigner::GetXFP(cvc) - Return the result as a Dart string
• Tapsigner::Xpub(cvc, master) - Same as GetXFP(cvc)
• Tapsigner::Pubkey(cvc) - Return the result as a Dart string
• Tapsigner::Change(new_cvc, cvc) - Return the response as a Dart struct
• Tapsigner::Backup(cvc) - Return the response as a Dart struct

Safe functions:

• Tapsigner::NeedSetup() - Cached
• Tapsigner::GetNumberOfBackups() - Cached
• Tapsigner::GetDerivationPath() - Cached