This commit provides a few fixes for the fullscreen view:
* make external links associated with a slide clickable again in fullscreen
mode;
* hide completion icons if not member:
* add margin to subquiz icon in header;
* add dedicated button to exit the fullscreen mode;
* change "Pass certification" button to "Test Certification" if not member
of the channel (for website publishers);
Commit linked to task ID 1941250 and PR #31977