- not send content is not validated and therefore not passed to server-side callback (currently only implemented for text-, select- and checkbox)
- new method et2_grid.getRow(_widget) to return a fake row container to pass it etemplate2.submit() --> implemented a real row-container for et2_grid
- new output_mode=4 for etemplate_new::exec() to force a json response, like form was submitted from client-side
--> allows to use full server-side validation for ajax like calls submitting only partial content
