Add lazy loading option to widgets

Change-Id: I24e5020dde42a02adea2276253b7b04207b7a4a2
diff --git a/dev/js/src/plugin/widget.js b/dev/js/src/plugin/widget.js
index 403954c..068ced4 100644
--- a/dev/js/src/plugin/widget.js
+++ b/dev/js/src/plugin/widget.js
@@ -35,6 +35,7 @@
         return this._load;
 
       let obj = this.load();
+      obj.setAttribute('loading', 'lazy');
 
       // Per default there should at least be a button
       // for settings, if the plugin requires settings.