Bug 21260: Introduce local pref to affect status grouping

Bug 21260: Introduce local pref to affect status grouping

Introducing a local preference Available_NFL to control which not for
loan statuses are considered to be 'available for reference'.
Standard value is '1|2' which comes down to the former >0 when using
the initial Koha defaults.

Test plan:
[1] Pick a biblio with an available item A, an item B with notforloan 1,
    an item C with notforloan 2 and two damaged items. (Former patch.)
    Include it in a OPAC search. You should see:
        Available: A. Reference: B, C. Not-available: Damaged(2).
[2] Add local pref Available_NFL with value '1'. Repeat the search.
    You should see now:
        Available: A. Reference: B. Not-available: S.C.(1), Damaged(2).
    [where S.C. stands for Staff Collection]
[3] Run test t/db_dependent/XSLT.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: ava li <rubyli208@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>