Revert playlist to original sorted order
Add option to revert a playlist to the original sorted order (the same order when drag-and-drop songs to a playlist).
1. What if you don't add songs all at once (pick and choose different songs by drag and drop)?
2. What if you open an existing playlist, and sort according to name. How do you restore the original sorting? You can't unless you reopen the same playlist again.
I think each playlist needs to have a song order property that shows the order of the songs in the playlist (it should be a number).