Bug 14589: Adjust authorities_merge_ajax and replace some indirect syntax

Bug 14589: Adjust authorities_merge_ajax and replace some indirect syntax

This patch does the following:
[1] Adjust authorities_merge_ajax just as in bug 14588.
[2] Replace some indirect syntax for fetch GGI::Cookie.
[3] Along the way replace some new CGI's. Note that I am not aiming to
    replace them Koha wide. The "fetch class" variant is less readable.

NOTE: The changes to tools/upload-file.pl and upload-file-progress.pl
are moved to report 14321.

Test plan:
[1] Run the URL authorities/merge_ajax.pl in staff.
[2] Upload a file with Stage MARC records for import.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
[1] It runs, but also before patch
[2] File uploads without problem
No errors

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
We could certainly remove 1 or 2 call to CGI->new in tools/background-job-progress.pl
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>