[#14] Adding percents after seeing results

Relative issue: #14

This issue was a pain at the beginning to understand.
I added 2 percents to the UI: 

 - percent of students completed
 - percent of students over 70% of correct answers

If I had to change something now in this issue, that should be simple to change since I understand how this thing works.

/!\ Warning: I erased some stuff to resolve conflicts. I have to restore it now