Add Video player page

[dan-niles]

This PR adds the video player for the new UI.

• Set up video.js with support for subtitles and variable playback rates.
• Added channel_description and channel_joined_date to the Author schema so that we can display channel information easily in the video player page.
• Included webp-hero for WebP support in unsupported browsers.
• Added a Cypress test for video player page.

Note: ogv.js has not been setup yet. I've created #230 to track it seperately.

Closes #215 Closes #174