Audio content type

Reuses the Video view

Refactored some of the names to 'Media', to make it more agnostic

NB, this is a basic start, more work to come styling up the control bar better

![screen shot 2014-07-28 at 12 14 32](https://cloud.githubusercontent.com/assets/74132/3719739/7559f51a-1648-11e4-8bb3-d935f5cdcf5e.png)

@mattosborn just so you know, the support for the `:not()` pseudo selector is not super good. Hopefully the UX does not depend on this CSS to be good.