bug 4396: clarify return of itemtype-level notforloan flag

bug 4396: clarify return of itemtype-level notforloan flag

* GetItemsInfo now includes a notforloan_per_itemtype key
  with the value of the item type's notforloan setting, correctly
  set based on the value of the item-level_itypes syspref
* Adjusted OPAC details item status display to use that
  notforloan_per_itemtype key

NOTE: one of the assumptions of item-level_itypes is that
      you can have either bib-level item types or item-level
      item types, but not both in the same database.  In particular,
      it does not establish a hierarchy where Koha checks the
      item-level itemtype first, then the bib-level.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>