Enhance Thermostat device: Window state

[Apollon77]

It was requested that also the connected Window state of the thermostat could be displayed.
This would mean to include a window state sensor state also optionally into the thermostat device ... In fact same discussion as in #87

[GermanBluefox]

I think it is impossible. Only if the state directly in device/channel. But normally it is outside

[Apollon77]

Homematic thermostat ... see last state

[Garfonso]

My first thought was that this probably is a bit redundant...

But on the other hand, most thermostats support some kind of "open window detection"... so... maybe this indeed makes sense.