REST: allow setting a member's moderation_action to None
A None value for a member's moderation_action has meaning now, but couldn't be set in the REST API. This MR makes it possible.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
A None value for a member's moderation_action has meaning now, but couldn't be set in the REST API. This MR makes it possible.