Example showing best-practise for handling device disconnection and reconnection

[hamishwillee]

We need to show how a user might best handle disconnecting from the vehicle and reconnecting, both when managing 1 vehicle and when managing multiple vehicles. I'd expect a client app to:

• be able to detect and report disconnection/connection
• stop the device from attempting to send messages
• reset to a sensible state based on what the vehicle is actually doing when you connect - e.g. if already flying, not attempt to send commands to arm etc (unless the vehicle ignores those).