Add Edit/Check-Mode after form-submit

When the User clicks the button to submit the form, they will be redirected immediately. 
It would be nice if they get the chance to check their input again and be able to edit something if there is a mistake.

- [ ] add check-mode
- [ ] edit option
- [ ] add sessions

For data security it would be good to add sessions to this aswell.
Might be to specify by @berlintam and @sareg0 ?