Auto cue split

- Attempt to split audio files by cue sheet during post processing,
requires shntools with flac or xld. If the split fails then the
directory is set as unprocessed.
https://github.com/rembo10/headphones/issues/1938

- last.fm album art/info - try with release id if adding album
manually. https://github.com/rembo10/headphones/issues/1923,
https://github.com/rembo10/headphones/issues/1871