* Allow domain blocks to reject media without silencing or suspending
* Fix typo
* Hide 'Reject media' button when superfluous, instead of disabling it
* Properly hide 'reject media' checkbox on page load if needed
This may happen when resubmitting the domain block form after an error.
* Don't ask whether undoing a media-only block should be retroactive
* Rename :media_only block to :noop
* Display :noop block as None in frontend, allow blocks that do nothing
* Remove 'coding' line auto-added by emacs
Create MediaAttachment but without actual file download when domain is blocked with reject_media set to true
Clean up old media files when creating a new domain block with reject_media set to true
Return remote_url in media attachments API if local file is not present
Undo domain block action in admin UI
Ability to enable reject_media from admin UI