Fix admin drilldown analytics chart behavior

[GUI]

In the admin analytics, the drilldown chart behavior can be a bit whacky, and isn't always correct. This is something I've noticed for a while, but never quite got around to figuring out why or when it misbehaves. I finally dug into this a bit more, and figured out the data for the chart was not always being cleared each time you drilled down another layer in the URL path hierarchy. So as you drilled down, the table of data below was always correct, but the chart above could end up with left-over data from the previous level. If you refreshed the page or applied new filters, the problem would disappear, so that's why it seemed somewhat sporadic.

[GUI]

And of course this weird behavior was fixed by a simple 1 line change (to add an option to tell the charting library to replace the data on changes, rather than trying to merge it): NREL/api-umbrella@53d263b