make album column for tracks configurable

introduces new config variable `album_column`

fixes #267

src/playlist.rs

@@ -128,7 +128,7 @@ impl ListItem for Playlist {
         self.name.clone()
     }
 
-    fn display_center(&self) -> String {
+    fn display_center(&self, _library: Arc<Library>) -> String {
         "".to_string()
     }