Broken the set theme logic from contnt portal provider

- Set theme logic is now handled generically in a request
  event listener.
- And renamed portal provider to content provider

Depends on: https://github.com/sulu-cmf/sulu-standard/issues/115
The PHPUnit mocker sucks and makes simple things like this complicated.. there is another library called Prophecy (part of PHPSpec). Might be worth discussing:

https://github.com/symfony-cmf/RoutingAutoBundle/blob/master/Tests/Unit/Adapter/PhpcrOdmAdapterTest.php