NetworkX provides `add_node`, we don't, leads to missing
`graph.node["vop"]`. Does this fix it?

We needed to implement `GraphState.from_json` so that the server can
track a copy of the client's state. That's a useful byproduct of this
work!

By default the server echoes messages to all clients.
The fancy.GraphState client was never calling ws.recv()
And hence a buffer was filling up somewhere
And we were hanging.
Adding a ws.recv() fixed the problem.

And we automatically pop a browser window when the server boots. Nice