/**
  * Initialize the plugin by loading admin scripts & styles and adding a
  * settings page and menu.
  *
  * @since     1.0.0
  */
 private function __construct()
 {
     /*
      * Call $plugin_slug from public plugin class.
      */
     $plugin = Responsive_IO::get_instance();
     $this->plugin_slug = $plugin->get_plugin_slug();
 }