Merge tag '0.2.1' into develop

0.2.1
-----

2017-07-17

* Now return media files with absolute URL
* Now display CLI instructions to download a set of tracks
* Fixed #33: sort by track position in album in API by default, also reuse that information on frontend side
* More robust audio player and queue in various situations:
* upgrade to latest dynamic_preferences and use redis as cache even locally