Add a user method to check folder permission

User model is the most natural place for a permission check method,
however this means that we need to pass the full user object to
service model methods and TemplateList instead of user_id.

app/main/views/conversation.py

@@ -52,7 +52,7 @@ def conversation_reply(
         templates_and_folders=TemplateList(
             current_service,
             template_folder_id=from_folder,
-            user_id=current_user.id,
+            user=current_user,
             template_type='sms'
         ),
         template_folder_path=current_service.get_template_folder_path(from_folder),