Add nodes by GUID in the GUI

Fixes #250 
oh, get_peers() doesn't do what I thought, not sure if it'd make sense to also do `self.client_peers(socket_handler, None)` right after, will that update the list of peers in the UI once the node has been found?

```
self. def client_peers(self, socket_handler, msg):
        self._log.info("Peers command")
        self.send_to_client(None, {"type": "peers", "peers": self.get_peers()})
```