[OE-4547] Remove code duplication from generic admin.
[OE-4547] Add support for SELECTION_LABEL_FIELD to generic admin.
[OE-4547] Break SelectionWidget list data code out into a separate helper class.
[OE-4547] Use SelectionHelper::listData in _generic_admin_lookup.
[OE-4547] Use SELECTION_ORDER rather than default scope in Subspecialty.