#3447 / Icons das man im FrontEnd direkt das gewaehlte FormElement im Formulareditor bearbeiten kann.
AbstractBuildForm.php: Add checkbox left to the 'EditForm'-Button to toogle the 'FormElemnt'-Icons -as the regular 'Form Edit'-Pencil, the 'FormElement Checkbox' is only displayed if the user is logged in BE.
BuildFormBootstrap.php: new function 'buildEditFormElementCheckbos()'