Bug 18426: Allow to edit subscriptions in batch

Bug 18426: Allow to edit subscriptions in batch

This adds a checkbox column in serials-search.pl tables that allow to edit
selected subscriptions.
The following fields can be modified:
 - Bookseller
 - Location
 - Library
 - Item type
 - Public note
 - Nonpublic note
 - "Create item when receiving" flag
 - Expiration date
+ the additional fields defined in serials/add_fields.pl

Test plan:

1. Go to Serials module
2. If there is no additional fields defined, define some (at least one with an
   authorized value and one without)
3. Start a subscription search
4. Select some results using the checkboxes and click the "Edit" button above
   the table
5. Select values for some fields (not all) and click "Start batch edit"
6. Verify you are being redirected to the previous search results
7. Verify that the fields for which you selected a value were modified and that
   the others fields weren't
8. Repeat steps 4 to 7 but this time, modify the other fields.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>