skip non downloadable tracks when downloading playlists. method rename.
Refactor.
Split 'common/' into commit '4385f041d59330788228b681fb2d67a95c324b40'

git-subtree-dir: common
git-subtree-mainline: 111c969e6679ec4c07fa465988f4b43eadbc049a
git-subtree-split: 4385f041d59330788228b681fb2d67a95c324b40