Elastic: Use appropriate icon for Mark button in "Mark all as read" dialog

program/js/app.js

@@ -4331,7 +4331,7 @@ function rcube_webmail()
             ref.mark_all_read(folder, $('input:checked', content).val());
             return true;
           },
-          {button: 'mark'}
+          {button: 'mark', button_class: 'save'}
         );
 
         return;

skins/elastic/styles/widgets/buttons.less

@@ -107,9 +107,6 @@ button.btn {
     &.cancel:before {
         content: @fa-var-times;
     }
-    &.mark:before {
-        .font-icon-regular(@fa-var-star);
-    }
     &.back:before {
         content: @fa-var-chevron-left;
     }