Bug 19837: Add multiple patrons to a list by barcode

Bug 19837: Add multiple patrons to a list by barcode

This patch adds the interface change and basic functionality for an
option to add multiple patrons to a patron list by scanning barcodes.

To test, apply the patch and go to Tools -> Patron lists.

- Create a patron list if necessary, and got to the "Add patrons"
  screen.
- Test the process for adding patrons using the "Patron search" text
  input.
- Test the process for adding patrons using the "Enter multiple card
  numbers" option.

This should really have some error-handling added to it: Onscreen
messages when a non-existing patron card number is submitted or when a
patron already exists on the list.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>