Bug 29634: Map biblio.medium to 245 by default (MARC21)

Bug 29634: Map biblio.medium to 245 by default (MARC21)

This patch adds a mapping from 245 to biblio.medium.

To test:
1) Apply patch
2) Delete existing frameworks
   -  In the database
      delete from marc_tag_structure;
      delete from marc_subfield_structure;
      delete from biblio_framework;
3) Load default framework
   - In a terminal, run
     ./misc/load_yaml.pl -f installer/data/mysql/en/marcflavour/marc21/mandatory/marc21_framework_DEFAULT.yml --load
4) In the staff interface, go to Administration > MARC bibliographic framework
   - Make sure the default framework is there
5) In Administration > Koha to MARC mapping, check the mappings for biblio.medium
   - biblio.medium should be mapped to 245
6) Create a bibliographic record with a value in 245
   - In the database, check the biblio entry for this record, the value from 245 should be in medium

I hope I didn't forget anything! :)

Caroline

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>