Bug 6831 follow-up: add support for UNIMARC and NORMARC

Bug 6831 follow-up: add support for UNIMARC and NORMARC

1) Removes unused subroutine get_host_control_num
2) Fixes small mistake, correct subfield for ISBN 020 is z
3) Checks system preference for correct marcflavour instead of
   assuming MARC21
4) Fixes MARC21 to not use author(), because it would also add
   fields like $w and $0 to 773$a
5) Fixes MARC21 to not use title(), but 245$a, because it would
   also add too many subfields.
6) Adds definitions for UNIMARC and includes NORMARC

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Works properly with all supported MARC flavours.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>