Bug 20468: Add multi-select to staff article request form

Bug 20468: Add multi-select to staff article request form

Adds a column with a checkbox. Adds buttons under the table for Select,
Clear and Actions menu.
An additional javascript function HandleMulti is placed between the form
and the functions handling individual requests.

Note: The Actions menu below does not contain Print slip. This does not
work in its current form. This could be handled on a separate report.

Test plan:
[1] Enable Article Requests. Add a few requests.
[2] Test the Select all / Clear all functionality on the form.
[3] Verify that the menu options Process, Complete and Cancel work as
    expected both from the individual Actions menu as from the shared
    Actions menu for selected requests.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Patch applies and functions as described.
Signed-off-by: Dilan Johnpullé <dilan@calyx.net.au>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>