Restapi/playlist

Creater restapi for playlist.
For info about restapi:
https://sat.inso.tuwien.ac.at/redmine/projects/qse-ase-ws14-11/wiki/Rest_API_Description

Restapi should be according to:
http://jsonapi.org/format/

I tested it with postman chrome, because at time of development, the infrastructure for mocca was not available
Here i´m updating a single ressource.
I respond with 404 if i cannot find the ressource the user wants to access (or do not have the access to it). Thus meaning: yep, i got your PUT request, it all went fine, but there is nothing i could "put"

I´m against upsert behaviour here because of the object_id creation.