[WFCORE-189] Provide a proper detail message when creating an OFE
Merge pull request #255 from bstansberry/WFCORE-189

[WFCORE-189] Provide a proper detail message when creating an OFE
[WFCORE-213] :  Clean unreferenced items from the content repository

Now we are using ContentReference to track contents in the content repository.
Now we are tracking references to overlays.
Trying to use server group definition for domain mode.
Simplifying ContentReference
Fixing overzealous cleaning of HC content.