Bug 27807: Add multi-column ordering support to datatables wrapper

Bug 27807: Add multi-column ordering support to datatables wrapper

This patch add mutli-column ordering support to the datatables api
wrapper.

Test plan
1/ Add a series of cities to the system with various combinations of
city and state such that you can distinguish sorting on city + state in
city ascending + state ascending, city ascending + state descending etc.
2/ Attempt to sort on the two fields in the table (Click the 'City'
heading to sort on city name, then Shift Click on 'State' to add 'state'
ordering on top.. Shift click again on state to reverse the 'state'
ordering but maintain the 'City' ordering.
3/ Confirm the various ordering comes out correctly.
4/ Signoff

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 548562ca17ae06088e84d8fe9287a9f4043ce80e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>