Support custom scale for series in graph.

[jd-boyd]

Currently in a line chart, I have one series that ranges 0 to 100, while another series ranges from 0 to 1 and yet another ranges from -1 to 1. The resulting graph isn't very useful. I could scale and offset the values of the [0,1] range and [-1,1] ranges, but then when the user hovers over a point on that line, they will see the wrong value.

I would either like to be able to specify a range when adding a series and have it scale like the secondary range does (AKA, to have more than just two ranges) or I would like to specify the displayed hover value separately from the rendered value per point (so it might render at 33, but when hovered over show a value of -1).