Move ValueTransformers to Extras/ directory. This is for stuff that is used by ProjectDemo and the test suite, and we can move to a separate CoreObjectExtras framework at some point.

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9794 7b3f36aa-e6db-49c1-8b4c-66eac1997e64