Bug 15766: Adding descriptions to patron card batches

Bug 15766: Adding descriptions to patron card batches

This patch adds a 'description' column to the creator_batches table. The
description for a batch can be added and updated using ajax.

To test:
1) Apply patch and update database (you will have to restart memcached)
2) Go to Tools -> Patron card creator -> Manage batches
3) There should now be a Description column next to Batch ID. This
will be empty (as none of the batches have descriptions yet)
4) Click Edit for any batch
5) Notice new Batch description text field. Enter a description for
the batch in here and click Save description. Some text should show
saying the description was saved.
6) If you go back to the manage batches page, the description should
now show under the Description column.
7) Go to Tools -> Label Creator -> Manage labels
8) Repeat steps 3 to 6

Sponsored-by: Catalyst IT
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>