Bug 9988: Add Koha objects for table need_merge_authorities

Bug 9988: Add Koha objects for table need_merge_authorities

This patch adds two Koha objects: MergeRequest(s).
MergeRequest has a new method and an oldmarc method.
A class method reporting_tag_xml is added to MergeRequests.pm.
All new routines are tested in Authorities.t.

Removes a few unneeded modules from Koha::Authority.

Test plan:
Run t/db_dependent/Koha/Authorities.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>