Bug 8000: Redirect all emails to SendAllEmailsTo

Bug 8000: Redirect all emails to SendAllEmailsTo

Rebased and squashed after changes to master.
Only difference from previous patches are small adjustements to conflicts in t/db_dependent/Letters.t

Test plan:

1) Apply path
2) Run updatedatabase.pl
3) Clear all SendAllEmailsTo system preference
4) Send mail to a patron of your choosing, email will go to patron's
   email address as usual.
5) Set SendAllEmailsTo to a test email address
6) Send mail to the patron, email will be redirected to the email set
   in the systempreference.
7) Run prove -v t/db_dependent/Letters.t

It does not affect messages in the message_queue.

This patch obsoletes previous patches, because it achieves the same
functionality in a much more centralized way. (4 lines of code!)

Signed-off-by: Ed Veal <eveal@mckinneytexas.org>
Signed-off-by: BWS Sandboxes <ByWaterSandboxes@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>