[FEATURE] Playing Next List (including queued)

[flxwu]

Subsequently to #96 , I would also love a "playing next" list in the right panel :)
I can also try implementing that if you don't mind 😄

[fabiofalci]

Of course I don't mind 😀

That panel I call the queue, but it only adds there if you queue the song manually. It make sense to extend that to have the next ones to be played, and if you queue a track, just adds in the top.

[flxwu]

Hey,
the last weeks I've been really busy, but now I wanted to build it, though I realized that I cannot generate a Spotify application key... thus, can I still build sconsify?