hideChannels: add /watch page functionality

[insin]

From a feature request thread on Twitter: https://twitter.com/Narull/status/1762343885790224709

• Allow a channel to be hidden from one of its videos - add a "Hide channel" menu item to the video's ᠁ menu

• If the user ends up on the /watch page for a video from a channel they hid (e.g. from their watch history, or an external search result, or if they have Auto-play enabled and it sent them there…), automatically pause the video and display some kind of overlay which needs to be clicked/tapped to remove the overlay and resume playing

  Un-hiding a channel while the overlay is displayed should also remove the overlay

[insin]

Moved my WIP on the auto-pause/overlay part of this into a branch for now, as it was becoming very fiddly for what is a nice-to-have feature, e.g.

• We don't know if YouTube will be able to auto play the video in the user's browser
• A pre-roll ad can start playing before the video starts playing
• An ad can start playing after we determined that we could paused the video after initial load

This makes it tricky to know when we should automatically pause the video, e.g. on initial load we have to wait for the video to start playing, but it might never do so, or an ad might start playing first, or the user might have initiated the initial play if their browser settings require an initial interaction before autoplay is allowed, in which case pausing would be the wrong thing to do

https://github.com/insin/control-panel-for-youtube/tree/hidden-channel-video-overlay

[realAzazello]

* [x]  Allow a channel to be hidden from one of its videos - add a "Hide channel" menu item to the video's  ᠁ menu

{You probably get this alot!} There's a userscript (and addon?) that already does
the hiding part (the unhiding has to be done manually):

Schegge's Block Youtube Users : https://github.com/Schegge/userscripts

as close as we're gonna get to a 'uBlock' for user accounts on YT.