Bug 19972: Make holds to pull list honors item-level_itypes syspref

Bug 19972: Make holds to pull list honors item-level_itypes syspref

And reflect that in the UI strings + variable names

Test plan:
1. Set syspref "item-level_itypes" to "specific item"
2. Create a hold on a record with one item
3. Change the document type of the item
4. Check that the item edition page and the record page show 2 different
     types.
5. Go to /cgi-bin/koha/circ/pendingreserves.pl
6. Check that the displayed type is the item one
7. Set syspref "item-level_itypes" to "biblio record"
8. Go to /cgi-bin/koha/circ/pendingreserves.pl
9. See that the displayed type is the item one. When the sysopref says
     "record"
     This is the bug.
10. Apply this patch
11. Go to /cgi-bin/koha/circ/pendingreserves.pl
12. See that the displayed type now follows the syspref
13. Set syspref "item-level_itypes" to "specific item"
14. Go to /cgi-bin/koha/circ/pendingreserves.pl
15. See that the displayed type still follows the syspref

Signed-off-by: Lucie Gay <lucie.gay@ens-paris-saclay.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>