[Bug 868455] Add custom combined hover class for graphs.

This is a completely custom rickshaw component designed to work with k.Graph. I referenced Rickshaw's HoverDetail while writing it, but it isn't a subclass like the other custom hovers that we used before.

I also unminified the `rickshaw.css` file so that I could read it, and combined the two other custom hover classes, since only the bar chart version was being used.

r?