New Function Suggest: Auto-detect port connectivity

[KemonDream]

• I spent a couple of days to digging out a way to connect my Audiogrid server, just found out that the firewall on the server was actuality blocking all the incoming connections.
  I tested all my device from my Macbook Imac, tried zerotier, wifi and ethernet cable connection. All failed before turn the damn firewall off.
• And like every time I click the "connect" button on the AudioGridder plugin window, no matter how hard I try, nothing shows up. It says "not connected" but the server menu show me three option "rescan", "wipe cache and rescan"and "reconnect", looks exactly likes the server is working fine. But the statistics shows 0kb and the same on the server's. No errors and no signs.
  The reason I tried that hard was because I do have made connected to the Grid Server somehow. So I assumed that my firewall was in a fine setting.
• Before long, I searched for similarly issues and read both server and plugin logs and found out that when the plugin make a connection the server got noting and also no any connection history in log files. Than I do some telnet things to determine whether the common port and high ports used by the server are open. The result is obvious, no port opened.
• Finally I just turned off the firewall so that everything looks smooth and clean.
• In the end, the suggest is that writing some error messages, warnings or making a one-click-ports-connectivity-check would be much appreciated and make the whole things easier.
  Anyway, this is a great project that connects everything together. Thank you for your hardworking and efforts on it!