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

mods/cnc/chrome/createserver.yaml

@@ -75,7 +75,7 @@ Container@CREATESERVER_PANEL:
 					Y:180
 					Width:300
 					Height:20
-					Text:Allow UPnP port forwarding
+					Text:Automatic port forwarding
 				Label@EXTERNAL_PORT_LABEL:
 					X:15
 					Y:219

mods/ra/chrome/create-server.yaml

@@ -65,7 +65,7 @@ Background@CREATESERVER_BG:
 			Y:165
 			Width:300
 			Height:20
-			Text:Allow UPnP port forwarding
+			Text:Automatic port forwarding
 		Button@CREATE_BUTTON:
 			X:130
 			Y:PARENT_BOTTOM - 45