Youtube and SponsorBlock Feature Enhancement

[cheintz]

I realize a lot of effort is likely going into countermeasures for server-side ads, and that this complicates SponsorBlock as well. That said, to achieve feature parity with ReVanced and NewPipe x SponsorBlock (now Tubular), I suggest the following enhancements to the youtube plugin and/or GrayJay:

• Allow seeking to start of chapters like the youtube app "chapters" menu
• When playing a video, playlist, or queue, make it clear in the UI that the video is downloaded and that the download is being played
• Allow download/deletion of individual videos from queue and playlist, without being actively playing the video in question.
• Show SponsorBlock segments in timeline. I believe this was planned (#377 ) but the previous request was closed before completion
• Allow submission of SponsorBlock segments
• Allow whitelisting of channels from SponsorBlock
• (new-to-class feature) Allow per-channel SponsorBlock segment type settings

[lemenn]

The whitelisting of individual channels/videos would also allow us to support creators without a warning telling us that we are depriving creators of revenue by enabling this plugin feature