backdropClass property

added backdropClass property to modal service settings

angular-ui-bootstrap/angular-ui-bootstrap.d.ts

@@ -264,6 +264,11 @@ declare module angular.ui.bootstrap {
          */
         keyboard?: boolean;
 
+        /**
+         * additional CSS class(es) to be added to a modal backdrop template
+         */
+        backdropClass?: string;
+
         /**
          * additional CSS class(es) to be added to a modal window template
          */