MQTT - higher level protocol

[mitra42]

Design and implement a higher level protocol incorporating for example

• Device announcement
• Pulling down a backlog of messages (e.g. after power or network loss)
• Getting a full rebroadcast of state.

[mitra42]

In active progress .... minor issues

• Get hostname and use as client id see issue 38 on Juerd's library.
  • add xWiFi::clientid
  • Add to mqtt connect
  • Use everywhere that currently use SYSTEM_DISCOVERY_DEVICE
• Consider moving to AsyncWiFiSettings port of it by @DTTerraStar it might handle the issue of trying to reconnect better and looks actively maintained.
• Move project etc description into config
• Think through SYSTEM_DISCOVERY_PROJECT
  • should this be in configuration,
  • or just second part (after dev/ or /)
  • or maybe first part in dropdown, and second part as string
  • and maybe use partner as userid for mqtt (and add to passwords file in ./html)