Feature/playlists

this adds the playlists to our app. some screenshots:
![playlist1](https://cloud.githubusercontent.com/assets/275897/5555072/a1c31c16-8c91-11e4-8281-7547e1354921.PNG)
![playlist2](https://cloud.githubusercontent.com/assets/275897/5555073/a316565a-8c91-11e4-93e4-045617a88077.PNG)
![playlist3](https://cloud.githubusercontent.com/assets/275897/5555074/a447fcea-8c91-11e4-85a5-ae29653a9d21.PNG)
![playlist4](https://cloud.githubusercontent.com/assets/275897/5555075/a4c2a9fe-8c91-11e4-97be-134091f2ce47.PNG)

without those lines, i could "give" a playlist from someone.
For example: i make a PUT request where the owner_id is  xyzand my id is xyz.

I update the playlist and set the owner_id to abc ... it goes through the validation and in the update statement, updates my playlist away from me to user xyz.

Not a very likely scenario, but get's away by the two deleted lines