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.