Add persistent storage for TopTracks

[peddybeats]

• Create db table UserTopTrack(userid, dateAdded, numTimesSeeded, track-uri)
• Create db table TrackFeatures(trackuri, feat1, feat2, feat3, feat4, feat5)
• Add create and read routines for it -- addTopTrack(userid, trackid, [features]) -- getTopTracks(userid) -> [{trackid, [features]}]

[peddybeats]

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