Support context brushing

[lkittock]

I would like a feature that allows filtering a chart the way some stock charts are filtered. Under the chart you have a second chart that contains the full range of data, with a little window that lets you move around and filter the data in the large chart, similar to how it is done in these two examples:

http://bl.ocks.org/mbostock/1667367
https://www.google.com/finance?q=NYSE%3AIBM&ei=xQEtV7DUMoK0mAHtza24DA