New Reporting Source for Hold/Copy Ratios
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A new reporting source is added, "Hold/Copy Ratio per Bib
and Pickup Library (and Descendants)", that, for each bib
that has a hold request on it or any of its components,
calculates the following:

 * active holds at each OU (including the OU's descendants)
 * holdable copies at each OU (and its descendants)
 * the ratio of the above two counts
 * counts and ratio across the entire consortium

This source differs from the "Hold/Copy Ratio per Bib
and Pickup Library" source by including all descendants
of the organization unit one is filtering on.

One use case is allowing a multi-branch system within an
Evergreen consortium that doesn't do full resource sharing
to readily calculate whether additional copies should be
purchased for that system.