Supports track and playlist downloads from SoundCloud URLs. (#HoleInOneHack)
Split 'common/' into commit '4b0277a34495b7ec99b49583382eeefd930f358c'

git-subtree-dir: common
git-subtree-mainline: 41d7f1e805935f10acbacfe305260b45877b3b13
git-subtree-split: 4b0277a34495b7ec99b49583382eeefd930f358c
skip non downloadable tracks when downloading playlists. method rename.