graph updates itself from a websocket

It does what it says it should, but there's lots of problems with this version:
- the svg is deleted and recreated from scratch every time; we should be using d3's .enter()/.update()/.exit() selections
- data is coming over JsonDataServer, which is not the newer WAMP server I figured out
- sped up JsonDataServer by 10 because the graph was loading realllly slow
- the graph needs "hysteresis" to be applied as suggested by mbostock -- changing the axes all the time is confusing to users
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