[MERGE] website_slides(_*): improve profile, lesson list display and demo data

This merge contains various improvements and fixes related to the new
eLearning application. Sub commits will give you more details on this
merge content as everything is not completely related.

Containing mainly
 * improve demo data to have more links and quizzes;
 * redesign the profile page, make it responsive and use bs4 when possible;
 * fix lesson list in training channels not displaying all slides;
 * improve lesson list design;

Merge linked to task ID 1941250 and PR #31453 about post-merge
cleaning and review.

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