Bug 18811: Add Koha Objects for authority tags and subfields

Bug 18811: Add Koha Objects for authority tags and subfields

Trivial copy and paste activity.
Will be used in a later patch.

No test plan needed.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit ca8f8b4cd91fac4acb6e2338720b8e0a82bce0b0)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>