add SensorMultilevel

[michapr]

Using HTTPDevice or CodeDevice it can be used to get values from MQTT server

[Edubits]

Thanks for the PR @michapr! Can you give an example use case where you want to set the value of a sensor?

[michapr]

For any external sensor - I have as sample 433MHz sensors, Bluetooth sensors, CO2, TVOC a,d PM2.5/10 WiFi sensors.
All of them are reporting to MQTT server.
Using a CodeDevice or HTTP Device I can integrate them into Z-Way. (is already working since some weeks here ;)...)

I want to extend the MQTT app more and forked your repo.