[Bandcamp] Fix link handler acceptance behaviour

* Test for bandcamp footer instead of meta tag (which is not present on
  all pages)
* Accept links to /music, not just /releases
* Correctly handle uppercase URLs

Necessary, because the external pages tested before were converted to bandcamp.com pages. See f9d06252

Add new exceptions to be able to display different error messages in apps

Unignore more tests

Bandcamp support

Use final where possible in YoutubeStreamExtractor and do some other code style improvements

AgeRestrictedException will be thrown only if the reason message equals to "Sign in to confirm your age" and if the age limit is 18.

The ContentNotSupportedException is thrown because no supported audio streams where extracted. However, SoundCLoud does not check, whether there are any streams available. 
This commit should be reverted in #526

Also check if related streams are empty if they are expected to be empty.

These exceptions are thrown on a test with the error messages text, because YouTube returns only "UNPLAYABLE" status in most error cases.
Tests are based with English strings, so changing the lang used by
extractor will throw the generic exception (ContentNotAvailableException).

Add GeographicRestrictionException and SoundCloudGoPlusException in NewPipe Extractor to be able to display different error messages

This commit adds two new exceptions in NewPipe Extractor: GeographicRestrictionException and SoundCloudGoPlusException (which extend to ContentNotAvailableException). These exceptions allow showing different error messages to user when a content isn't available in his/her/its country (only used for now by SoundCloudStreamExtractor) or when the content is a SoundCloud Go+ track.

Fix YouTube channels contination

[youtube] improve comments extraction performance

Update extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeCommentsExtractor.java
Co-authored-by: Tobi <TobiGr@users.noreply.github.com>

[SoundCloud] Update client_id and fix extraction

- do not parse responseBody twice for continuation
instead try to get commentsTokenInside with the new pattern ("sectionListRenderer")
and try again with the old pattern ("commentSectionRenderer") on failure
- do not unescape responseBody multiple times
   -> parse responseBody less times

Fixes missing comments under videos

Because it's unused with the new request.
Co-authored-by: bopol <bopol@e.email>

Co-authored-by: TiA4f8R <74829229+tia4f8r@users.noreply.github.com>

SoundCloud changed their Javascript structure. That caused the client_id to be in the middle of the file (at byte ~43000 ). To have a little buffer, we now fetch the first 50000 bytes.

Playlist continuations