Calculated Proximity Adjustments, a new feature

Calculated Proximity Adjustments, a new feature

Allows customization to the way that Evergreen measures the distance
between org units for the purposes of 1) determining what copy at what
org unit is best suited for targeting a title-level hold, and 2)
determining what hold is best suited for fulfillment by a copy-in-hand
at capture (checkin) time.  The customization is based on a table
'actor.org_unit_proximity_adjustment', with certain matching criteria
that the system compares to properties of the holds and copies in
question.

This feature is actually side-ported from the FulfILLment project, where
it was originally developed by Mike Rylander.  Lebbeous Fogle-Weekley
was responsible for integration into current Evergreen code, some
testing and bug-fixing, and minor refinement of documentation.

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>