Implement Scrobble buffering/retrying

db/migration/20210623155401_add_user_prefs_player_scrobbler_enabled.go

@@ -40,6 +40,5 @@ alter table player add scrobble_enabled bool default true;
 }
 
 func downAddUserPrefsPlayerScrobblerEnabled(tx *sql.Tx) error {
-	// This code is executed when the migration is rolled back.
 	return nil
 }