add a 'backoffice' variable for site template

extra/modules/root.ptl

@@ -860,6 +860,10 @@ class AlternateRootDirectory(OldRootDirectory):
         self.announces()
         '</div>'
 
+        user = get_request().user
+        if user and user.can_go_in_backoffice():
+            get_response().filter['backoffice'] = True
+
     def services [html] (self):
         template.html_top()
         get_response().filter['bigdiv'] = 'rub_service'