add recentTimestamp and give md_expectations a default expectation for unknown keys
add recentTimestamp and give md_expectations a default expectation for unknown keys

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