COPersistentRoot: add a  property, which is a thin wrapper around the  property. Reason for adding is both Typewriter and ProjectDemo have incompatible homegrown versions of this idea, and probably every application will need it. NOTE: as mentioned in the comment, I don't know whether we should call this , , , etc... It's called  to match COObject's -name.

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10575 7b3f36aa-e6db-49c1-8b4c-66eac1997e64