add rickshaw gem

Rickshaw is a JS data visualisation tool.
change graph functions to work with rickshaw
graph exchanged for rickshaw
Still no fill-between. May need to write in plain D3.js like http://bl.ocks.org/mbostock/3884914
ignore dump files
Change time tick density on x-axis
Changes graph so that it is readable
Show direction on graph with arrows
Merge branch 'rickshaw-graphs'