Added retriever plugin
Merge pull request #114 from mexon/retriever

Added retriever plugin
Merge remote-tracking branch 'upstream/master'
Now you can depublicise as well as publicise.  Plus you can select whether comments should be on or off, and how long articles are left before expiring.
Now depublicising marks users as expired rather than deleting them straight away, and recycles them if they are re-publicised