Bug 28286: show "Place hold" button if item is holdable

Bug 28286: show "Place hold" button if item is holdable

This patch adds "filter_by_for_hold" method in "Items.pm" and
uses it in "cat-toolbar.inc" instead of "filter_by_for_load".

Also this patch removes "filter_by_for_loan" method.

To reproduce the bug:
1) go to /cgi-bin/koha/catalogue/detail.pl?biblionumber=XXX	that has
item with notforloan value set as "Ordered" (-1)
2) see that button "Place hold" is not present
3) apply the patch
4) refresh the page and ensure that "Place hold" button appears even if
item is "Ordered"

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>