Bug 6520: Display items for staged record

Bug 6520: Display items for staged record

When records are imported into Koha, the items is stored into the
import_items table.
This marcxml in this table is never retrieved to display items.

Test plan:
1/ Import a records with items
2/ Before importing the batch into the catalog, you can see the marc
of the records, in the table below.
3/ Verify that the items is correctly displayed.

QA note: This patch does not provide test for new subroutines but the
module (C4::ImportBatch) is not tested at all and it will be time
consuming to provide them.

Signed-off-by: Nicole Engard <nengard@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>