Add all other recipients of initial mail into notification list
    
Whenever a customer is writing an email and is putting further
addresses into CC, we assume those are interested in the whole
correspondence as well, so put them into the notification list.
Not all recipients from initial mail are put on notification list on ticket creation

When a new mail is put into the system, on ticket creation only the To: email
address is put into the notification list, other contacts put into Cc: are
ignored. But usually this is not the intention of the author.

So on ticket creation all recipients should be put into the notification list
of the new ticket.

fixes launchpad bug https://bugs.launchpad.net/eventum/+bug/1002203