/**
  * Returns and/or create the single instance of this class.  
  *
  * @return  Charitable_Email_Settings
  * @access  public
  * @since   1.2.0
  */
 public static function get_instance()
 {
     if (is_null(self::$instance)) {
         self::$instance = new Charitable_Email_Settings();
     }
     return self::$instance;
 }
 */
add_filter('charitable_settings_tab_fields_licenses', array(Charitable_Licenses_Settings::get_instance(), 'add_licenses_fields'), 5);
/**
 * Add settings to the Advanced tab.
 *
 * @see     Charitable_Advanced_Settings::add_advanced_fields()
 */
add_filter('charitable_settings_tab_fields_advanced', array(Charitable_Advanced_Settings::get_instance(), 'add_advanced_fields'), 5);
/**
 * Add extra settings for the individual gateways & emails tabs.
 *
 * @see     Charitable_Gateway_Settings::add_individual_gateway_fields()
 * @see     Charitable_Email_Settings::add_individual_email_fields()
 */
add_filter('charitable_settings_tab_fields', array(Charitable_Gateway_Settings::get_instance(), 'add_individual_gateway_fields'), 5);
add_filter('charitable_settings_tab_fields', array(Charitable_Email_Settings::get_instance(), 'add_individual_email_fields'), 5);
/**
 * Add the PayPal sandbox testing tool to the gateway settings page.
 *
 * @see     Charitable_Gateway_Settings::render_paypal_sandbox_test()
 */
add_action('charitable_after_admin_settings', array(Charitable_Gateway_Settings::get_instance(), 'render_paypal_sandbox_test'));
/**
 * Redirect the user to PayPal for the sandbox test.
 *
 * @see     Charitable_Gateway_Settings::redirect_paypal_sandbox_test()
 */
add_action('charitable_do_paypal_sandbox_test', array(Charitable_Gateway_Settings::get_instance(), 'redirect_paypal_sandbox_test'));
/**
 * Redirect to the PayPal gateway settings after being returned from PayPal.
 *