When a description is missing, no description should be returned, even the ones
indicating there is no description. This behavior is represented by a null
return instead.
Also update PeertubeAccountExtractorTest to reflect these changes.
* Deprecated Utils#UTF-8; see StandardCharsets
* Added more helpful methods to ``ExtractorAsserts``
* Use parameterized (cool new) tests
* Restore functionality of some tests + updated mockdata
* Other code cleanups + Sonarlint improvements
* Rename PeertubeUserExtractor to PeertubeAccountExtractor
* Add test for video-channels in PeertubeChannelLinkHandlerFactoryTest
* Compatibility support for older versions (use "accounts/" as default)