Refactorize StoredObjectVoter.php

The StoredObjectVoter.php has been refactorized to handle context-specific voters.\
This way we can check if the context-specific voter should handle the authorization or not.\
If not, there is a simple fallback to check on the USER_ROLE.

src/Bundle/ChillDocStoreBundle/config/services/voter.yaml

@@ -0,0 +1,14 @@
+services:
+    _defaults:
+        autowire: true
+        autoconfigure: true
+    Chill\DocStoreBundle\Security\Authorization\StoredObjectVoter:
+        arguments:
+            $storedObjectVoters:
+                # context specific voters
+                - '@accompanying_course_document_voter'
+        tags:
+            - { name: security.voter }
+
+    accompanying_course_document_voter:
+        class: Chill\DocStoreBundle\Security\Authorization\AccompanyingCourseDocumentVoter