Generic temp sensor node

[mhaack]

Hi,

I have seen the reused BME280Node and there is also a DHT22Node. Maybe we can refactor them a little to have some abstract "environment sensor" node as a common base. The could also host the constants from constant.h.
I have some SHT3x temp & humidity sensors here and would also create a node class. So there would already be three use cases.

WDYT?

[luebbe]

Sounds good. IIRC I came across a generic environment sensor on github a while ago, but I can't find it right now.