Fixed some design issues, implemented more playback-controls

And here I am again with another PR (it seems that I really seem to like your project...).
Things I did:
* Updated Bootstrap to v3
* implemented better playback controls
* switched to the bootstrap grid system
* implemented now playing status
Because I changed a lot of the design, here are some screenshots:
![](http://puu.sh/80Fhh.jpg)
![](http://puu.sh/80FiV.jpg)
![](http://puu.sh/80Fjw.jpg)
![](http://puu.sh/80FkO.png)
![](http://puu.sh/80Fm3.jpg)