Handle deleted/terminated YT channels

[stephanebruckert]

To fix:

• it should not alter the YT "total" tracks
• mark as terminated

To add:

• update the playlist desc
• tweet about it

[stephanebruckert]

Handled: terminated channels now show as 'Archived' on the frontend, Spotify playlists get renamed with (Archive) suffix, thumbnails are repaired from Spotify covers, and the frontend shows a placeholder for broken images.