Bug 14321: Introduce Koha::Upload

Bug 14321: Introduce Koha::Upload

This patch introduces Koha::Upload. It will replace the modules
C4::UploadedFile.pm and the new C4::UploadedFiles.pm (from BZ 6874).
It also includes a new unit test.

NOTE: This unit test will replace the test for UploadedFiles.pm. It will no
longer use dependency Test::CGI::Multipart. We are now mocking CGI and its
hook to achieve the same result.

Test plan:
[1] Run t/db_dependent/Upload.t.
    Note that if you see a WARNING, you will still need to add an entry
    upload_path to your koha-conf.xml. Or you need to give write
    permission to your Koha instance user for that folder.

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>