Public Form should show a "successfully submitted" page

[sleidig]

After submitting a Public Form, the user can see a small toast message at the bottom of the screen but also immediately gets a new, empty form again. The message is easy to overlook and people may get confused if the form was really saved. It will be better to display a full screen "Your data was successfully submitted" page (with a link to "submit another form" that re-opens the empty form view)