Bug 26195: Add a way to specify authorised values should be expanded [OAI]

Bug 26195: Add a way to specify authorised values should be expanded [OAI]

This patch introduces a new configuration entry for OAI so the resulting
records include authorised value descriptions instead of codes.

This is off by default.

To test:
1. Create a yaml file with the extended OAI configuration
2. Visit http://kohadev.myDNSname.org:8080/cgi-bin/koha/oai.pl
3. Browse some records
=> SUCCESS: The fields tied to AV show codes.
4. Update your configuration with 'expanded_avs: 1' for one  of the
   defined format like in:

  ---
  format:
    marc21:
      metadataPrefix: marc21
      metadataNamespace: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim
      schema: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim.xsd
      include_items: 0
    marcxml:
      metadataPrefix: marcxml
      metadataNamespace: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim
      schema: http://www.loc.gov/MARC21/slim http://www.loc.gov/standards/marcxml/schema/MARC21slim.xsd
      include_items: 1
      expanded_avs: 1
5. restart_all
6. Repead 3
=> SUCCESS: AV descriptions are returned!
7. Sign off :-D

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>