#2542 / FormElement-Typ 'note' funktioniert nicht mit dynamic update

''abel' and 'note' are fixed - 'value' is still not updated, open.
HelperFormElement.php: buildFormElementName() had some issue if there was no $formElement[FE_NAME] defined. New workaround: take the $formElement[FE_ID] instead.
AbstractBuildForm.php: creation of JSON has been missed - now fixed. The $value is rendered (recent value), but probably the client is not prepared to update a non-HTML-input field. This has to debug with RO.