Implement Threshold feature about kiwi-air-monitor HOT 3 CLOSED

Color options from: https://personal.sron.nl/~pault/

or one of these without the reds:

from kiwi-air-monitor.

To detect a decreasing trend I compare the current (1 minute wide rolling mean) CO2 value, and compare that to the max value the past half hour. I consider it decreasing if it's closer than 50% of the threshold.

I suspect that we'll need to tweak this logic in the future, as when you get closer to the threshold, the sensitivity between level 1 and 2 changes.

from kiwi-air-monitor.

First version is done, for now it works, later we might need to update it with a better way to detect the downwards trend

from kiwi-air-monitor.