Bug 13353 - changelog update specifically for the 3.18 release

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Release notes for 3.18.0

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Translation updates for Koha 3.18.0 release
Increment version for 3.18.0 release

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>