Bug 20017: use Modern::Perl in Tools perl scripts

Bug 20017: use Modern::Perl in Tools perl scripts

Test plan:
Check that the following files don't contain use strict; use warnings;
and have use Modern::Perl instead.
background-job-progress.pl
batchMod.pl
copy-holidays.pl
exceptionHolidays.pl
holidays.pl
import_borrowers.pl
koha-news.pl
letter.pl
manage-marc-import.pl
newHolidays.pl
overduerules.pl
quotes-upload.pl
quotes.pl
quotes/quotes-upload_ajax.pl
quotes/quotes_ajax.pl
scheduler.pl
stage-marc-import.pl
upload-cover-image.pl

Also the credits have been added to newHolidays.pl

Signed-off-by: Jon Knight <J.P.Knight@lboro.ac.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>