introduce persistent data storage, which for now just caches rom -> server pairs

MultiServer.py

@@ -519,6 +519,7 @@ class ClientMessageProcessor(CommandProcessor):
             notify_all(self.ctx, get_players_string(self.ctx))
         else:
             self.output(get_players_string(self.ctx))
+        return True
 
     def _cmd_forfeit(self) -> bool:
         """Surrender and send your remaining items out to their recipients"""