Bug 17737: Replace GetReservesFromItemnumber with Koha::Item->get_holds_placed_before...

Bug 17737: Replace GetReservesFromItemnumber with Koha::Item->get_holds_placed_before_today

On the same way of Koha::Biblio->get_holds,
Koha::Biblio->get_holds_placed_before_today and Koha::Patron->get_holds,
this new subroutin will permit to retrieve the holds placed on a
specific item.
Note that at the moment we do not need a Koha::Item->get_holds method:
we do not want to display future holds placed in the future.

Test plan:
I would suggest to test this patch with patches from bug 17736 and bug 17738,
to place different kind of holds (biblio and item level, future and
past).
Then do a whole workflow to detect bug, view a record, delete record,
order, place a hold on an item which has been ordered, etc.
The hold's informations should always be the same without or without
these patches.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>