Bug 11880: Select the barcode index by default then searching for label items.

Bug 11880: Select the barcode index by default then searching for label items.

Test case:
* Go to "Tools -> Label creator -> Manage batches"
* Click on the "New batch" button
* Click on the "Add item(s)" button
* A search window should open. The "Barcode" value should be selected in the the selectbox.

Followed test case. Patch behaves as expected.
Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>