Bug 11351 - Add support for SIP2 media types

Bug 11351 - Add support for SIP2 media types

Koha's SIP2 server implementation does not currently support the SIP2
protocol field "media type" ( CK ).

This patch implements the SIP2 media type by allowing an arbitrary
mapping of itemtypes to SIP2 media types.

Test Plan:
1) Apply this patch
2) Run updatedatabase
3) Edit an itemtype, select a SIP media type, and save the changes
4) Make a SIP2 Item Information Request
5) Verify that the CK field of the Item Information Response contains
   the correct media type code.

Signed-off-by: Benjamin Rokseth <benjamin.rokseth@kul.oslo.kommune.no>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>