Bug 29570: Enable sorting orders by summary

Bug 29570: Enable sorting orders by summary

This patch enables (on receiving) sorting orders by the summary column.
It needs the previous patches to work. Title is given more precedence as
expressed by users on the bug report. Which, by the way, makes sense.

To test:
1. Create a basket
2. Create orders
3. Close basket
4. Receive shipment
5. Enter invoice information
=> SUCCESS: You should see your pending orders
=> FAIL: Verify the 'Summary' column is not sortable
7. Apply this patches
8. Restart Plack
9. Reload the page
=> SUCCESS: Can sort by the summary column
10. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>