start of big MARC21 authorities work

start of big MARC21 authorities work

* Defined local field 942$a to store the authority type
  for MARC21 instead of 152$b
* Added 942$b to MARC21 authority framework.
* Added auth_header.authid and auth_header.authtypecode
  to appropriate subfields in MARC21 authority framework.
* Started work on two new modules:
    C4::AuthoritiesMarc::MARC21
    C4::AuthoritiesMarc::UNIMARC
  These modules will be used to extract MARC-format-specific
  behavior out of C4::AuthoritiesMarc
* Updated Zebra config for MARC21 to use only the 942$a
  for the authority type.
* For MARC21, added logic to move 152$b to 942$a for
  existing authority records.  Specifically, AddAuthority
  now does this move when a record is saved, while
  GetAuthority and GetAuthorityXML do this when
  extracting a record for other use.  This logic
  is temporary, and can hopefully be removed later, once
  use of 152$b in MARC21 authorities is confirmed to be
  absent for Koha users.  I will also create a batch
  job to do this update in one fell swoop.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>