[feature request] Image popularity chart

[Jack Ireland]

As well as actual usage, we could also measure and display how popular image requests are in a two week window. We'd look at the data requests from Helioviewer.org and JHelioviewer, make a note of all the combinations, and then count the number of occurrences of those combinations. In this view, AIA 304 is a different request from a overlay of AIA 304 and AIA 171. These requests are counted separately.

This would be useful in assessing the popularity of datasets, and how they are combined. Further, we could breakdown the popularity by JPX, helioviewer.org and screenshot request. It would be useful to express the results as both numbers and percentages. i.e., what percentage of JPX requests in the last two weeks were for AIA 304?