/**
  * Returns a singleton of the gallery mapper
  * @param string $context
  * @return C_Gallery_Mapper
  */
 public static function get_instance($context = False)
 {
     if (is_null(self::$_instance)) {
         $klass = get_class();
         self::$_instance = new $klass($context);
     }
     return self::$_instance;
 }