add subjectToCuration and metajamId as immutable md keys
add subjectToCuration and metajamId as immutable md keys

peetahzee/Unofficial-Google-Music-API,nvbn/Unofficial-Google-Music-API,TheOpenDevProject/gmusicapi,dvirtz/gmusicapi,jimyx17/gmusic,tanhaiwang/gmusicapi,dvirtz/gmusicapi,simon-weber/gmusicapi,thebigmunch/gmusicapi,simon-weber/Unofficial-Google-Music-API