[Feature] Backup server address

[Randomblock1]

I have my Pi running as my music server, and I use Subtracks to play over LAN. I also have a VPN setup so I can access it anywhere, but I have to switch it every time. I remember Substreamer had support for 2 IPs, and while Subtracks makes it easy to just switch servers, it would be real neat to have it seamlessly just work.

It should try to use the main (local) address, and time out after a short duration, like 1 second, then use the backup (public) address. Check every few seconds, or use ConnectivityManager.NetworkCallback to monitor for network changes (or something like that).

I wouldn't call this high priority, it's just nice to have.