[REF] website_slides: revamp fullscreen widget

This commit makes the 'Fullscreen' page a complete odoo
widgets. We decided to split it into some sub widget:
- Fullscreen: will be the master piece, handle communication of
components, displaying slide content, setting slide as completed,
handling server RPC calls, ....
- Sidebar: responsible for slide navigation, based on the table of
content. (prev, next, keyboard naviguation, ...)
- VideoPlayer: display content for Youtube video and handling player
event to auto set as completed, ...

The DOM of this page is still rendered serverside. DOM was cleaned in
order to be less complex and less deep. CSS style was also reviewed
to decrease line of code.

Fullscreen is now completely using Quiz widget with events triggered.

Task-1942852