Bug 20076: Add syspref to remove overdues notification by email to staff if user...

Bug 20076: Add syspref to remove overdues notification by email to staff if user has no email address

I took the same test plan as victor but I added the system preference to manage the case more easily, especially for users who do not have access to the koha server.

Test plan
1. Check the size of the message queue
     With the following SQL query (using an SQL report if you want)
     SELECT COUNT(*) FROM message_queue;
2. Run misc/cronjobs/overdue_notices.pl
3. Check the size of the message queue
     To ensure that no other overdues will create noise in this test plan.
     Or you can take them into account.
4. Choose a patron with no email address
5. Create an overdue (checkout an item and unfold "Checkout settings"
   and set a date in the past which is compatible with what you find in
   staff:/cgi-bin/koha/tools/overduerules.pl
6. Run misc/cronjobs/overdue_notices.pl
7. Check that you have two new messages in the queue
8. Inspect these two messages
   SELECT * FROM message_queue ORDER BY time_queued DESC LIMIT 2 \G
   1. One has the type "print" and the borrowernumber matching the patron.
   2. The other has
        subject: Overdue Notices
        borrowernumber: NULL
        message_transport_type: email
        and contains "These messages were not sent directly to the patrons."
        This is the one we don't want anymore.
        Because it's now obsolete due to the first message.
9. Apply this patch
10. Run updatedabatase.pl
11. Change syspref 'EmailOverduesNoEmail' to "Don't send"
12. Delete data from message_queue (if you have access) for a cleaner view
13. Run again misc/cronjobs/overdue_notices.pl
14. Check that only the print message is now generated and not the
      "Overdue Notices" one.

https://bugs.koha-community.org/show_bug.cgi?id=20076

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>