Eliminate all uses of the IShopRoot interface.

Instead we use the navigation root to register views
that are supposed to be shop-global. This will make
ftw.shop work with subsites that are supposed to
have "their own shop".
BugFix: If the fullname of a logged in user had umlauts the form was broken.
BugFix: It's possible to have users wihtout a fullname: For example SystemUsers / ldap users.