Completions tab - add plots of scans vs. time

[jcf2]

1. One item of interest for a new plot is the % of subjects who had a CUFF1 scan who go on to get a CUFF2, tracked by site over time. The field Acquisition Date would provide the date for this, rounded to the prior Monday.

2. Another interesting plot that might go in that tab for lack of a better place could be a simple look at Acquisition Date itself (i.e. "scans per week"). We can get a plot of this from the Imaging Log currently, where a current view looks like this:
   

On the Imaging Log this can't be broken down by site/MCC (or narrowed to a date range), which would be nice. Though the date entries are collapsed to the week level it's still a bit noisy, and would be more so by site.

3. Display "surgery interval" (surgery date minus scan date) by site, e.g. in boxplots. NOTE: this may not be workable with our date rounding (both Surgery Date and Acquisition Date are rounded to the nearest week). We might precalculate this value and export it, though, so leaving it here as an idea.

4. Add and plot a "days since site's first scan" variable comparatively across sites. This could plot the cumulative number of scans against weeks of scanning. This could be on Completions.

(If there are enough of these, I suppose there could be a new panel for timeline type plots, though maybe that would be getting to be too many panels.)