Add information to exam / summary submission

One-sentence description

Add some confirmation message when submitting an exam.

Motivation

Currently there is no confirmation when you submit an exam + it doesn't show up in the list of exams immediately because there's a review first. This way it is not clear whether the submission was actually performed correctly + people don't know that an submission is manually checked before being published.

Desired functionality

Inform people whether their submission was succesful and why it isn't immediately visible.

Suggested implementation

Show a message thanking someone for their submission, also informing them that it will be published after a review.