Sparkline for real time module

Pivotal: https://www.pivotaltracker.com/s/projects/911874/stories/53309579

The sparkline here is slightly different from the designs: we don't use a tooltip, and we use axis labels at the top and bottom of the graph, not at the end points. This has been okayed with design. 

If we have time, I'd like to pair with Ben to improve the performance of hover events on these graphs - I think the current performance is acceptable, but could be improved.