[IMP] website_slides: allow to create and update quizzes directly in frontend

Purpose is to ease designing your courses by allowing to create and update
slide quiz directly in frontend, within the slide display.

With this commit you are able to

  * add a quiz to a slide or add a question to an existing quiz;
  * edit an existing question from a quiz:

   * change the title of the Question;
   * add, remove or update answers;
   * change the right answer;
   * delete an existing question;
   * reorder the questions from a quiz;
   * reset the quiz for the current user if he is a website designer, allowing
     to test the quiz and its answers;

New frontend widgets are introduced allowing to manipulate quiz. Slide page
now supports a readonly / taking quiz mode and an edit mode for quizzes
used notably for website designers / course maintainers.

Task ID : 1999636
PR : #35326

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