enhancement: "status-update" messages sends an empty status on trx disconnect

[gx1400]

When listening for status-update packets, and trx disconnects (like trx being powered off), the status message is empty.

Received message from server: {"request":"status-update","from":"ft-817","status":[]}

Recommend status of "disconnected" or something similar.

[mbalmer]

Yes, this, and make the list of destinations dynamic. Inform clients of new or disappearing devices.