Bug 20783: Use iframe to embed Youtube videos

Bug 20783: Use iframe to embed Youtube videos

WWW::YouTube::Download is broken and not reliable.
Other alternative was to use HTML::Video::Embed but not updated since
years.

The best alternative seems to follow youtube advise and use an iframe
https://developers.google.com/youtube/iframe_api_reference

Test plan:
Put youtube video in 856$u (using different url formats, youtu.be,
youtube.com/embed, etc.)
Enable HTML5MediaEnabled and HTML5MediaYouTube and confirm that the
youtube videos are correctly embeded.

Signed-off-by: Kelly McElligott <kelly@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>