Actually happened in previous commit, can't be bothered to amend

Added some more terms to clifford.by_name to ease lookup of complex
conjugates

Added GraphState.toggle_edges(), used by GraphState.measure_x

Nearly finished GraphState.measure_x

Made sure that `graph.js` dumps old graphs after use, and ensured that
`examples/stress_test` shuts down the connection after use (don't create millions
of clients).

Got rid of all the debug harness and refactored graphstate.py

Next up: measurement
Also added a test on local complementation

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

But it is not symmetric. I wonder why. Can run with either for now.