/**
  * Marks the order as not seen
  * 
  * @return void
  *
  * @author Sebastian Diel <*****@*****.**>
  * @since 14.03.2013
  */
 public function markAsNotSeen()
 {
     if ($this->IsSeen) {
         $this->IsSeen = false;
         $this->write();
         SilvercartOrderLog::addMarkedAsNotSeenLog($this, 'SilvercartOrder');
     }
 }