request: Add {playlist_track_num} to track template variables

[cjl4hd]

I would like being able to download playlists as-is, in the order that I created them in Spotify. This way it will be possible to save each playlist in its own folder and easily playable in the order of the original playlist.

[Rafiuth]

This already exists as {context_index} (you might be interested in {context_name} as well). Note that it will ignore column sorting and output 0 for tracks added in the queue.

Ref: #16