Bug 23114: Inventory: allow to scan barcodes

Bug 23114: Inventory: allow to scan barcodes

This patch allows the user to scan barcodes in the inventory tool
(in addition to upload a barcode file, like in other tools)

Test plan:
 1) Apply the patch.
 2) Check that you can still upload a barcode file.
 3) Check that you can scan/enter barcodes in the new textarea.
 4) Check that if you both upload a barcode file and enter barcodes,
    you will be prompted to choose only one method.
 5) Check that you can then proceed to the next step by either resetting the
    upload file input or emptying the textarea.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>