Rest GET

This PR aims to:
- GET a resource by FOSRest

Notes:
- When you get the error `The controller must return a response (Object(Acme\BlogBundle\Entity\Page) given).` you need to add the FOSRest Configuration to `app/config/config.yml`
- to test the API you just need to run `curl -S http://xxxx/web/app_dev.php/api/v1/pages/1.json`