This PR adds two new config option, to pass a PO token (config 'po_token') and
a visitor ID (config 'visitor_data') to Youtube. These two strings are required
to play videos using the WEB client.
Warning: These strings gives much more identifiable information to Google!
If the po_token setting is filled in, then the WEB client is used. If not, the
Android client is used. TvHtml5ScreenEmbed will still be used as a fallback.
Script for generating po_token and visitor_data:
https://github.com/iv-org/youtube-trusted-session-generator
Helps with issue 4734
2d18ff1f80