Gapless playback

[robbevp]

When playing an album that is supposed to be one long track (for example, Toman's Where Wolves Wear Wolf Wear), a user will notice a gap between the tracks.
This gap is caused by a combination of three things:

1. Waiting for the currentTrackURLto reflect the new track
2. Loading the track
3. Waiting for the API to calculate the length of a track that is converted

I don't think we can/should try to fully eliminate the gap, since we'll always depend on some JS events and are dependent on the users internet connection (and the speed/internet connnection of the API). But I'd like to figure out If we can get closer to gapless playing - especially by eliminating 2 & 3.

I'm currently thinking of having a currentTrack and a nextTrack so we can start preloading the audio when the currentTrack is fully loaded - other suggestions/ideas are welcome.