Add support for OpenRTX radios

[hmatuschek]

This requires a lot of work (in openrtx branch):

• Implement OpenRTX codeplug encoding/decoding
• Implement interface to OpenRTX radios
• Implement M17 Channels
• Implement M17 Contacts
• Implement M17 RadioIDs
• Fix YAML generator/serializer
• Fix GUI
• Fix AnyTone codeplug generation to tolerate M17 elements.
• Fix TyT codeplug generation to tolerate M17 elements.
• Fix Radioddity codeplug generation to tolerate M17 elements.
• Update documentation