Fix onclick to keep originally bound click handler context.

Fixes app.appname.func callbacks had widget as context

api/js/etemplate/Et2Widget/Et2Widget.ts

@@ -234,7 +234,7 @@ const Et2WidgetMixin = (superClass) =>
 				var args = Array.prototype.slice.call(arguments);
 				if(args.indexOf(this) == -1) args.splice(1, 0, this);
 
-				return this.onclick.apply(this, args);
+				return this.onclick(...args);
 			}
 
 			return true;