feat: store and use m3u files on filesystem for playlists

closes #306
closes #307
closes #66

db/migrations_old_models.go

@@ -0,0 +1,20 @@
+package db
+
+import "time"
+
+type _OldPlaylist struct {
+	ID         int `gorm:"primary_key"`
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+	User       *User
+	UserID     int `sql:"default: null; type:int REFERENCES users(id) ON DELETE CASCADE"`
+	Name       string
+	Comment    string
+	TrackCount int
+	Items      string
+	IsPublic   bool `sql:"default: null"`
+}
+
+func (_OldPlaylist) TableName() string {
+	return "playlists"
+}