LP#1815815: Library Groups

LP#1815815: Library Groups

This branch implements Library Groups (what used to be called "lassos") for
Evergreen.

Evergreen has, internally, a concept called "lassos" that allows an
administrator to define a group of org units to search that has no relation
to the hierarchical org tree. For instance, one might create a group of law
or science libraries within a university consortium, or group all school
libraries together.

In addition to the previous always-visible type of Library Group (lasso), one
can now make them context-aware so that that only show up if the current
search location is included as one of the org units in the Library Group.
This is implemented without regard to the org unit hierarchy, and so requires
that the relevant ancestor and descendent org units be included in the group
along with those that actually hold copies, but allows for complete
flexibility in context-aware Library Group configuration.

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