Idea: “Stale” state option

[danricho]

It would be cool if we could report sensors as stale when they are not updated after a definable time.

My use case:
I have a battery operated pool temperature sensor which sends temperature readings and whether it's battery is low via this plugin to show as a temperature sensor and a contact sensor (batt low).
If the gadget isn't able to connect for some reason (eg: wifi is down or water has leaked into it), I will never know it isn't updating homebridge.

Thanks for the great plug-in. I wish I knew about TypeScript and was able to contribute.