Set up a new JobItemCart instance.
Will load the queue from the session or initialize a new one if nothing has been stored yet.
public function __construct() {
if (!isset($_SESSION[$this->session_key])) {
$_SESSION[$this->session_key] = [
'queue' => [],
'processed' => 0,
'destination' => NULL,
];
}
$this->queue =& $_SESSION[$this->session_key]['queue'];
$this->processed =& $_SESSION[$this->session_key]['processed'];
$this->destination =& $_SESSION[$this->session_key]['destination'];
}