[WFCORE-213] :  Clean unreferenced items from the content repository

We are using ContentReference to track contents in the content repository.
Se are tracking references to overlays.
Trying to use server group definition for domain mode.
Simplifying ContentReference
WFCORE-211: Fixing overzealous cleaning of HC content.
WFCORE-178: ContentRepositoryImpl should not call File.deleteOnExit

Jira: https://issues.jboss.org/browse/WFCORE-213
and https://issues.jboss.org/browse/WFCORE-211
and https://issues.jboss.org/browse/WFCORE-178
This is actually a bit different than I thought.

First, there's no need to remove a content reference for the thing that was replaced, as this handler does not remove that resource, it just changes its 'enabled' attribute.

Second, the add of the ContentReference for the replacement only needs to happen if the code in L110-114 that creates a new resource executes. Otherwise, there should already be a reference added by whatever op created the resource that's already there.

The add of the reference should happen in a ResultHandler though.