Ref T6916. Added video to remarkup using D7156 as reference.
- Viewed video files (MP4, Ogg) in Safari, Chrome, Firefox (some don't work, e.g., OGG in Safari, but nothing we can really do about that).
- Used alt.
- Used autoplay.
- Used loop.
- Used media=audio.
- Viewed file detail page.
- Handle maybe-audio, maybe-video files (like "application/ogg").
- Clean up display of file properties in Files ("Image", "Audio", "Video", etc) a little.
- Add media for media="audio", to explicitly render ambiguous files as audio.
- Clean up and document attributes.