Bug 21573: Move lists barcode and biblionumber entry form to modal

Bug 21573: Move lists barcode and biblionumber entry form to modal

This patch modifies the staff client lists page so that the
barcode/biblionumber entry form from the left hand sidebar into a modal
window, triggered by a button in the toolbar.

To test, apply the patch and rebuild the staff client CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

 - View the contents of a list in the staff client, logged in as a user
   who has permission to add items.
 - Click the "Add items" button. A modal window should appear with the
   barcode/biblionumber entry form.
 - Submit barcodes and/or biblionumbers and confirm that the correct
   titles are added to the list.
 - Log in again as a user who does not have permission to add to the
   list. Confirm that the button isn't present.

Signed-off-by: Mackey Johnstone <mackeyfj@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>