piano: Add error message for code 1039

See #352.
Stop playback if audio file is not accessible

See #352.
Transform actual station when loving/banning songs

Loving/banning a song from a shared station while playing quickmix
resulted in “call not allowed”, because we tried to transform the
quickmix instead of the song’s real station. Fixes #354.
Fix station name when deleting a station
Merge remote-tracking branch 'promy/master'