Typewriter: make it possible to create new tag groups. add context menus. (new tag groups aren't persisting, for some reason)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10243 7b3f36aa-e6db-49c1-8b4c-66eac1997e64