Bug 24588: Prevent e-mails from Koha to be flagged as spam

Bug 24588: Prevent e-mails from Koha to be flagged as spam

Set the e-mail headers Mailer-X and MessageID by Koha,
to gain a better positive score from the spam filter.

To test:
1) Let Koha send an e-mail message.
2) Check the header of this e-mail message with your e-mail client.
   There should be no X-Mailer header with value 'Koha'. If there
   is an MessageID header, it is probably set by the MSA, e.g. Exim.
   Example:
      Message-Id: <E1iyZRY-0006XT-0t@FQDN>
3) Apply patch.
4) Repeat step 1.
5) Check the header of the new e-mail message with your e-mail client.
   There should be a X-Mailer header with value 'Koha' and a MessageID
   header with a value set by Koha.
   Example:
      X-Mailer: Koha
      Message-Id: <15807387030.B731e.18490@FQDN>
6) Sign off.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>