Add picture node to user template

app/views/api/v1/users/base.json.rabl

@@ -3,6 +3,12 @@ object :user
 attributes :id,
     :username,
     :granblue_id,
-    :picture,
     :language,
     :private
+
+node :picture do |u|
+    {
+        :picture => u.picture,
+        :element => u.element
+    }
+end