COEditingContext code cleaning and reorganization

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9805 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
Forgot to commit a missing forward class declaration

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9806 7b3f36aa-e6db-49c1-8b4c-66eac1997e64