enhanced UPnP discovery usability

- don't search for NATs forever, 5 seconds seem to be enough
- disable the UPnP checkbox if discovery failed
- no computer industry acronyms in user GUI
- don't remove port-forwarding twice, just once on shutdown
- user-configurable settings for debugging

OpenRA.Game/Server/Server.cs

@@ -80,8 +80,6 @@ namespace OpenRA.Server
 		{
 			foreach (var t in ServerTraits.WithInterface<IEndGame>())
 				t.GameEnded(this);
-			if (Settings.AllowUPnP)
-				RemovePortforward();
 		}
 
 		public Server(IPEndPoint endpoint, string[] mods, ServerSettings settings, ModData modData, INatDevice natDevice)
@@ -159,6 +157,8 @@ namespace OpenRA.Server
 					if (State == ServerState.ShuttingDown)
 					{
 						EndGame();
+						if (Settings.AllowUPnP)
+							RemovePortforward();
 						break;
 					}
 				}
@@ -166,9 +166,6 @@ namespace OpenRA.Server
 				foreach (var t in ServerTraits.WithInterface<INotifyServerShutdown>())
 					t.ServerShutdown(this);
 
-				if (Settings.AllowUPnP)
-					RemovePortforward();
-
 				preConns.Clear();
 				conns.Clear();
 				try { listener.Stop(); }