Bug 15933: Add cataloguing plugin to search for existing publishers in other records

Bug 15933: Add cataloguing plugin to search for existing publishers in other records

This patch adds a new cataloging plugin for MARC21 installations,
marc21_field-260b.pl. When enabled it provides autocomplete for
publisher name, pulling existing data from biblioitems.publishercode.

To test, apply the patch and enable the plugin:

- Go to Administration -> MARC bibliographic framework -> MARC structure
  -> 260 -> Edit subfields -> Subfield b -> Other options.
- Set "Plugin" to marc21_field_260b.pl.
- Go to Cataloging and edit or create a record.
- Under tab 2 click the field for 260$b. Start typing a publisher name.
  A dropdown should appear with matching publishers.
- Selecting one of the results should populate the form field with that
  information.

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Also works with 264$b.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>