Serializer 0.12

uses #382 as a basis

this is will lead to a minor BC break:
```
-        $view->setSerializerVersion('2.1');
-        $view->setSerializerGroups(array('data'));
+        $context = new SerializationContext();
+        $context->setVersion('2.1');
+        $context->setGroups(array('data'));
+        $view->setSerializationContext($context);
```

Furthermore the default version/groups will now only be applied if no ``SerializationContext`` was explicitly set.