Let any 'admin' user elevate to 'root' for full system access

But otherwise, let the Administrator role be "normal" and have perms of
its own.  Hopefully cuts down on unwanted screen noise for admins.

tailbone/app.py

@@ -106,11 +106,22 @@ def provide_postgresql_settings(settings):
     settings.setdefault('tm.attempts', 2)
 
 
+class Root(dict):
+    """
+    Root factory for Pyramid.  This is necessary to make the current request
+    available to the authorization policy object, which needs it to check if
+    the current request "is root".
+    """
+
+    def __init__(self, request):
+        self.request = request
+
+
 def make_pyramid_config(settings):
     """
     Make a Pyramid config object from the given settings.
     """
-    config = Configurator(settings=settings)
+    config = Configurator(settings=settings, root_factory=Root)
 
     # Configure user authentication / authorization.
     config.set_authentication_policy(SessionAuthenticationPolicy())