Ensure that various rules set a reason.

Fixes #368 (closed)

Several rules do not set a moderation_reason resulting in holds and rejects with reason "N/A". This MR adds moderation_reasons and where applicable moderation_sender and moderation_action to the various rules than can cause a message to be held, rejected or discarded. It also adds tests for moderation_reasons being set.

Some of these attributes are not currently used in all these cases, but I don't think it hurts to add them in case we want to implement increased logging in the future.

Note: I have unchecked Remove source branch when merge request is accepted. in case that helps with possible backporting.