Add running average to time series visualization

[nmalkin]

In addition to just showing the value on the given date, there should be a second line representing the average of that value over the preceding 7 days.

For clarity (so that it's actually useful), this should only appear when the data is shown cumulatively (no segmentation), as a line.

(for Dan)

[vthunder]

Hmmmm sure?

Or cumulative with the running average as a line, that should also work (right?)

[nmalkin]

I'll try a couple of things, see what works.