Bug 19955: Add ability to process only one 'type' of message ( sms, email, etc )...

Bug 19955: Add ability to process only one 'type' of message ( sms, email, etc ) for a given run of process_message_queue.pl

It would be nice to allow emails to be sent overnight, but limit the sending of SMS messages to hours when people are awake. Adding a type limit to process_message_queue.pl would allow this to be accomplished easily.

Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>