Add "up next" view

[jgoguen]

When playing songs (by tapping a song, by pressing Play, or by pressing Shuffle), the current song appears in Now Playing. There is no way to see what song is up next.

[eeston]

I have a branch with this in progress. The Apple Music UI for up next requires quite a few animations to tie in together so it will require a little bit of work.

At the moment, playback issues are my priority