sensors: ignore individual measurements above treshhold

[markus2330]

unfortunately there are some glitches in the analog/digital converter, which needs some post-processing.

The sensor module should not trigger immediately if a single measurement is across a threshold. Furthermore it should not immediately forget about its state when a single measurement is below a threshold.

I now connected a Pt100 sensor with the sensors module, which works (except of this bug) great. Here the temperature measurements of the last days:

You can easily spot the individual spots, which imho shouldn't have lead to a warning.