LP#1795906: Allow more configuration of queue position calculation

LP#1795906: Allow more configuration of queue position calculation

Here we convert the global flag to a YAOUS that allows each library to specify
a "sharing depth" for hold queue position as shown to the patron.  Staff
retain direct control over the context of this calculation by means of an org
selector in the relevant UIs.

Values of note for the YAOUS:
 * Completely unset: restrict peer holds to the context hold's pickup library
 * Depth == 0: Treat all holds as queue peers, regardless of pickup library

Signed-off-by: Mike Rylander <mrylander@gmail.com>