Bug 26132: Remove raw sql query

Bug 26132: Remove raw sql query

Making use of Koha::Checkouts make the code much more readable here.
It fixes 2 flaws:
 * $type was not quote escaped
 * the effective itemtype was not used which could lead to wrong
 calculation (for instance item-level_itypes is set but the item does
 not have the itype defined)

However there is something to note, we are going to make things a bit
less effective as we are now fetching the items to get their effective
itemtype (vs a SUM done at DB level)

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>