[Feature] Auto shut down when in IDLE for 'x' minute

[GianCann]

If the hub is not running any user programs and is not connected to other devices, it may shut down itself to prevent battery drain (after 5 minutes in idle mode, for example.

[laurensvalk]

On Prime Hub, the status light turns off as expected but the light matrix stays on (until you remove USB). If the light happened to be on, it stays on also. Motors and sensors also remain powered.