Queue management

just what it sounds like. similar to simplenews features that allow the monitoring of send progress, although it would be nice to allow deletion of records as well.

quick thought: deletion would have to be a queued process as well, marking the row for deletion and a check/drop run before each cron mailing process if possible.

some type of notice on the management page saying the deletion will be attempted before next run but the mail to that sender may already have begun to be processed.. and a follow up success/failed "deleted before sent" or "revoked" noted in the record as well.. it could possibly take 2 cron runs to delete a record and know if a deletion was done before the mail was sent ("successfully revoked") because of the possibility of concurrent cron runs and error/issue checking...