GS dependencies: only install p.a.dexerity once.
GS dependencies: install p.a.registry only once.
GS dependencies: install opengever.base only once.
GS dependencies: install opengever.mail as toplevel dependency.
GS dependencies: install opengever.tabbedview as toplevel dependency.
GS dependencies: reduce dependencies on opengever.trash and opengever.dossier
GS dependencies: reduce dependencies to opengever.ogds.base.
Merge pull request #559 from 4teamwork/jone-tests

Optimize Generic Setup dependency graph