Save track queue when closing and restore at start

src/playable.rs

@@ -8,7 +8,8 @@ use crate::traits::{ListItem, ViewExt};
 use std::fmt;
 use std::sync::Arc;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Deserialize, Serialize)]
+#[serde(tag = "type")]
 pub enum Playable {
     Track(Track),
     Episode(Episode),