Parascope: remove usage visualizations

[jenniferlin15]

Since we have no usage for any of the CrossRef data, all the usage visualizations (both bubble charts) will look very strange. This may very well be a temporary issue since 1) we may get a new source - PMC Usage that will impact a subset of the CrossRef corpus and 2) we are redoing all the visualizations at the moment.

Until either change, I'd like to suppress the bubble charts all together or, if the work entailed is very minor, remove the usage dimension on the bubble charts, making bookmarks or citations serve as the Y-axis.

[jure]

I wanted to try this out the other day, but it seems that det.labs.crossref.org is down for some reason. I haven't done anything special to the visualizations to account for CrossRef missing data or CrossRef data in general, so it would be good to be able to try it out and see what still fails.

[mfenner]

Let me check on this tomorrow.