Extract playlists description

[ChunkyProgrammer]

• I carefully read the contribution guidelines and agree to them.
• I have tested the API against NewPipe.
• I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

This PR adds a getDescription method for playlist extraction + tests for the description. I am not planning on creating a PR in NewPipe to support this (I implemented this to hopefully add this to the Piped API)

API changes

This PR adds

• PlaylistExtractor.getDescription() and the corresponding PlaylistInfo.getDescription()
• PlaylistInfoItemExtractor.getDescription() and the corresponding PlaylistInfoItem.getDescription()

[AudricV]

Thanks, you need to also implement these changes in PlaylistInfo.

[TobiGr]

Thanks, you need to also implement these changes in PlaylistInfo.

I already implemented that locally. There are a few more changes which I am going to push within the next days.

[TobiGr]

@fynngodau I am unsure which parts of the album description should be used as description. Can you give me an advice?
My current plan is to add .tralbum-about, .tralbum-credits and #license.

Outdated review

[AudricV]

I am unsure which parts of the album description should be used as description.

When looking at the website, Bandcamp seems to unify everything you added, but on the mobile Android app, credits are separated in a credits section and the copyright does not appear.

I think we should follow this behavior, as credits and copyright are not parts of a description.

[fynngodau]

The copyright text is debatable because the individual tracks also always have copyright info, so it is not strictly necessary here and could be removed. The credits otoh should be read out here, as long as there's no separate method getCredits.