docs: def get_config_class(settings):
      """
      According to **settings.CONFIG_CLASS** return either config class
      defined by user or default :class:`shelter.core.config.Config`.
      """
      config_cls_name = getattr(settings, 'CONFIG_CLASS', '')
      if config_cls_name:
          config_cls = import_object(config_cls_name)
      else:
          config_cls = Config
      return config_cls