Add option to suppress feedback messages

This is used to dynamically exclude some test results from being shown to users, but still allows them to run in the background (e.g., for research).

app/controllers/concerns/file_parameters.rb

@@ -34,7 +34,7 @@ module FileParameters
 
   def file_attributes
     %w[content context_id feedback_message file_id file_type_id hidden id name native_file path read_only role weight
-       file_template_id]
+       file_template_id hidden_feedback]
   end
   private :file_attributes
 end