YouTube comments killer troch snek

This version now hides the comments completely, because trying to still show the comment submit section was highly unstable (because YouTube's dynamic website shenanigans made it *very* difficult).

By making this change the addon also requires less permissions (the browser activity permission was to detect when the site was changed through clicking the back button, because that changed the way the site was displayed; this is not needed anymore now, because the logic to just completely hide the comments is way easier).