Functionality for viewing saved tracks

[fdeitylink]

Fixes #69

Allows you to view a list of your saved tracks.

[danielfm]

This is nice!

The only feature I miss is to paginate new tracks by typing l, just like tracks on a playlist, etc.

Ref: https://github.com/danielfm/smudge/blob/master/smudge-playlist.el#L27