Add disabled state (and L&F) to gauge

[ArdJonker]

Sometimes a gauge is temporarily "not applicable" and then the look and feel should represent this. It seems logical to use a "disabled state" for this situation even though the gauge is not actionable (a thus can not be disabled).
Normal L&F:

Disabled L&F:

(This is but a rough example)

[leon-v]

This would be nice. I use one for the frequency of my solar power Inverter, which at night looks like a big error.

[phsdv]

I would like this too. I have a sensor that is not always on. When it is not on, the data the sensor returns is 'None'. When the gauge sees 'None' or other non numerical it should go to the disabled state. Now I get an error like this one: "Entity is non-numeric: sensor.c700_v2_0406_volume" instead of a Gauge (that is disabled)