Newpipe: Subtitle download support

[gabriellluz]

• [X] I carefully read the contribution guidelines and agree to them.
• [X] I checked if the issue/feature exists in the latest version.

Currently, when we download a video, we can't have the subtitles embedded in the video.
So we think we should have an option download subtitles in the same folder as the video or a ZIP file with all the subtitles including the auto-generated subtitles. I know muxing into a MKV might get tricky since NewPipe is for small to big mobile devices and most are really slow so I think downloading subtitles separately in the same folder or all of them in a ZIP would be easier.

[theScrabi]

sounds like a cool idea :)

[MissBastet]

yesssss I moved on to newpipe when tubemate stopped letting you download copyright videos but I am hard of hearing and I do miss the option of downloading videos with cc. currently you can watch the videos with them but not downlaod them with them :(

[theScrabi]

There is a contribution for subtitle downloading open right now. I will take care of it soon.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[TobiGr]

Implemented by @kapodamy in #1759