Be more explicit about consequences of completing a session

Just same as starting a session, rules need to warn student before they submit the final result. For example:
- When only one session is allowed, warn that if they do not submit, they will graded when the session is due and be grade according to the saved answers. And, if they press submit, warn that they won't have chance to start a new session, then give a chance for them to confirm.
- When they have chance to start new sessions, display how many times they can restart, and display the grade strategy message.

Thanks!