Removing the parent object of attachments causes the exception which prevents the deletion of the attachment.
This PR will delete the attachment if the parent is deleted.
Fixes editing attachment when the parent is missing
Fixing deleting attachments when the parent is missing
Fixing editing attachment when ContentType does not exist anymore
Fixing deleting attachment when ContentType does not exist anymore
Coloring rows of "unfindable" parents to red in attachment list view
Fixing accessing API of the attachment if the parent or its content type is missing
Automatically deletes the Attachment if the Parent object is deleted
Removing the parent object of attachments causes the exception which prevents the deletion of the attachment. This PR will delete the attachment if the parent is deleted.