youtube: size of the video element

[peterpeterparker]

The "Youtube" template display a YouTube video in a slide parsed with a 16/9 size.
This size is applied to the element and Youtube afterwards calculate automatically a video size inside this element in order to respect the video ratio.

Therefore it doesn't make that much sense to display the element in 16/9. Instead of this, the size should be the maximum size available (1/1).