creating entity repository for users

I also re-arranged the configuration of repositories to a dedicated file, which should improve readability.

Resources/config/services/repositories.yml

@@ -0,0 +1,12 @@
+services:
+    chill.main.countries_repository:
+        class: Doctrine\ORM\EntityRepository
+        factory: ["@doctrine.orm.entity_manager", getRepository]
+        arguments:
+            - "Chill\\MainBundle\\Entity\\Country"
+            
+    chill.main.user_repository:
+        class: Doctrine\ORM\EntityRepository
+        factory: ["@doctrine.orm.entity_manager", getRepository]
+        arguments:
+            - "Chill\\MainBundle\\Entity\\User"