Introduced NowPlayingRepository. Don't do anything for now

engine/nowplaying.go

@@ -0,0 +1,14 @@
+package engine
+
+import "time"
+
+const NowPlayingExpire = time.Duration(30) * time.Minute
+
+type NowPlayingInfo struct {
+	TrackId string
+	Start   time.Time
+}
+
+type NowPlayingRepository interface {
+	Add(trackId string) error
+}