Example for boiler and thermostat combi with MQTT

[dannyverp]

It would be nice if we could get an example that combines the MQTT with the external thermostat as well. I've been trying for days now to get this to work (shout-out to @compihu for the PlatformIO fork) but I'm going nowhere fast. I'm basically looking to combine this repo where you use the boiler and thermostat shields together and the current repo where you hook up the boiler to MQTT.