Admin features

Added following functions to the pb.AdminNavigation

    pb.AdminNavigation.add(node)
    pb.AdminNavigation.addChild(parentId, node)

addChild can be called at any time even before the parent tree node exists, this is just in case someone will ever need to do something like this. The navigation will only be built once on startup so the overhead should be really low.

i also added an adminSample Plugin to show off the admin related features.
I don't believe this works because the removeUnauthorized does not create a new navigation object it modifies the one passed in.  Passing in the singleton navigation structure would result in missing items for an admin user if a writer, for example, had logged in ahead of him.  In addition, we wanted to be able to support localization on a per request basis.  This doesn't happen if the navigation is only built once at startup.