Add deletion queue worker

Problem/Motivation

While the Orange Dam module creates items in a queue for items deleted at source, those items are not processed in any way.

Steps to reproduce

Queue deleted items. Run cron several times. See that the queued items do not disappear and nothing is deleted.

Proposed resolution

Create queue worker that will process deleted keywords and deleted content.

Remaining tasks

Document how an end user could override the default queue worker timing, to customize for their use-case.