serializer on accompanying course

Two new routes:

* `GET /{_locale}/person/api/1.0/accompanying-course/{parcours_id}/show.json`: get a json representation for a course
* `POST /{_locale}/person/api/1.0/accompanying-course/{parcours_id}/participation.json`:
add a particitipation to course. Usage:

    `curl -v --cookie "PHPSESSID=fed98aa23e40cb36e630f84155aea3bb;" -X
POST --data '{ "id": 481 }'
http://localhost:8001/fr/person/api/1.0/accompanying-course/270/participation.json`

    Will add the person with id "481" to the course.

src/Bundle/ChillMainBundle/config/services/serializer.yaml

@@ -0,0 +1,13 @@
+---
+services:
+    Chill\MainBundle\Serializer\Normalizer\CenterNormalizer:
+        tags:
+            - { name: 'serializer.normalizer', priority: 64 }
+
+    Chill\MainBundle\Serializer\Normalizer\DateNormalizer:
+        tags:
+            - { name: 'serializer.normalizer', priority: 64 }
+
+    Chill\MainBundle\Serializer\Normalizer\UserNormalizer:
+        tags:
+            - { name: 'serializer.normalizer', priority: 64 }