[IMP] website_slides: add comments on answers showed after answering a quiz

PURPOSE :

A quiz after a course content is a good way to check if the user gets the previous lesson.
Despite, the user/student may not understand why his answer was wrong/correct.
In this task we'll allow the teacher to add a comment next to the asnwer of a quiz.

SPECIFICATION :

The quiz creator will now be able to comment the answers to inform the frontend user why
his answer is wrong/correct. He will be able to add the comments both in backend and frontend.

Task ID : 2072566
PR : #41188

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>