[IMP] website_slides: add progressbar and completed tag

- Teacher can now see the progress of his students on the attendees' list.

- The completion of a course was recomputed even if the course is completed
  now it's fixed to 100 when completed.

- Added a progressbar in course page in front-end to allow the user to see
  it's progression. When completed, the tag completed is displayed instead of
  the progressbar.

- On slide page in front-end(normal view or fullscreen) when a course is
  completed, display the tag completed instead of the progressbar.

- Removed completed state on course "Taking care of Trees" for portal user
  because it was not the case.

task-2049689

closes odoo/odoo#36608

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