bit better right pane layout

src/public/javascripts/widgets/collapsible_widget.js

@@ -58,11 +58,16 @@ export default class CollapsibleWidget extends TabAwareWidget {
         this.$headerActions = this.$widget.find('.widget-header-actions');
         this.$headerActions.append(...this.getHeaderActions());
 
+        this.decorateWidget();
+
         this.initialized = this.doRenderBody();
 
         return this.$widget;
     }
 
+    /** for overriding */
+    decorateWidget() {}
+
     /** for overriding */
     async doRenderBody() {}