Move -undo, -redo, -canUndo, -canRedo to COTrack protocol. I thought they were already there but looks like we forgot about them.

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9967 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
CoreObject.xcodeproj: Make all headers public for now (this includes some that should really be private, we can fix it later)

git-svn-id: svn://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@9968 7b3f36aa-e6db-49c1-8b4c-66eac1997e64