Bug 27266: Move GetMarcAuthors to Koha namespace

Bug 27266: Move GetMarcAuthors to Koha namespace

This patch moves C4::Biblio::GetMarcAuthors to
Koha::Biblio->get_authors_from_MARC. This is so the method can be
used in templates and notices.

To test:
1. Find a record that has an author in the added entry field (700-720).
2. Add the record to the cart and a list.
3. View your cart and click 'more details'. Confirm authors show as
normal.
4. Click 'send' and confirm the email sent shows the authors as normal.
5. Go to the list you added the record to and click 'send list'. Confirm
the email sent shows the authors as normal.
xslt)
6. Log in to the OPAC. Find the record and add it to the cart and a list
7. View the cart and click 'more details'. Confirm authors show as
normal.
8. Click 'send' and confirm the email sent shows the authors as normal.
9. Go to the list you added the record to and click 'send list'.
Confirm the email sent shows the authors as normal.
10. Confirm tests pass:
- t/Biblio.t
- t/db_dependent/Koha/Biblio.t

Sponsored-by: Bibliotheksservice-Zentrum Baden-Württemberg (BSZ)
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>