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 like being ale to show how this is done.  The part I'm hesitant on is the extra plugin in the core.  Would you be opposed to adding this into the sample plugin that already exists instead?  Feel free to add yourself to the contributors list :)