Health status of homebridge visible in UI

[epheterson]

It'd be nice to have a little red / green dot beside the 'hub' in the UI to indicate if it's running well, or is currently unloaded. If it's unloaded, clicking on the red dot would offer to start it. If it's green, clicking on the green dot would offer to restart it.

I'm not sure if it's possible to detect unhealthy states of homebridge, for example if it's currently hung / crashed, though if so, it'd be nice to reflect that as orange/red, encouraging the user to address it.