Webplayer can now handle a basic playlist, pushing multiple songs in the
playlist and passing from one song to another.
Some things that are not yet working:
* Using previous and next buttons and going outside of the playlist
breaks things.
* Random / repeat modes are not yet implemented.
* Playlist is not exposed in the UI at the moment.
* Seeking in a song is not exposed in the UI.
* When playing a song, webplayer does not automatically play the next
one when reaching the end of the song.
* Keep track of pagination in the store
* Use Immutable in reducers
* Finish i18n, every available strings are now translated in English and French
* Add a loading indicator
* Premises of API error handling
* Better locale negotiation
