fix left alignment issues of artist name and tracks on mobile

Please check @MorrisJobke @jbtbnl @wakeup 

Before (everything at their own left starting position):
![screenshot from 2014-04-11 08 53 47](https://cloud.githubusercontent.com/assets/925062/2676992/f675bec4-c146-11e3-9269-ef70ac472b0a.png)

After (artist name aligned with covers, tracks aligned with album title – which they are sub-items of):
![screenshot from 2014-04-11 08 59 06](https://cloud.githubusercontent.com/assets/925062/2676994/fcbe20c8-c146-11e3-9f48-724debd576a9.png)