Navigation with progress blobs

This version allows you to :

* Answer questions in sequence : 1,2..

* Answer questions in any order.

* You can return to a previously-answered question. The previous answer
is displayed.

* You can change a previously-answered question.

* The progress blobs show answered-questions in green. The current
question is show with a black border.

* Once all questions have been answered, the outcome screen appears.