PURPOSE
This commit adds some small UI improvements to the e-learning views.
All those small changes are meant to improve the general user experience when
adding content to a course.
DETAILED SPECS
- Change some placeholders / labels
- Inform the end-user that he can edit his 'webpage' slide using the editor
- Inform the end-user that he can add questions to his 'quiz' slide using the
'Quiz' tab in the backend form view
- Do not update from slide metadata if field value is already set
- Do not allow previews for certifications
- "Allow Download" of slide content is now False by default
As it was nice to have for "Documentation" courses but does not really make
sense for "Training" ones.
- Having a duplicate video id is now informative on the frontend and not
blocking as before (it was allowed in the backend form anyway).
- Show the video title in the frontend preview
Task-2510174
Part-of: odoo/odoo#71477
Aurélien Warnon
ffa504887d