Streamline isVisible() and isAccessible implementations
Currently Node::isVisible() will only consider if a Node is accessible or not, if the security context is already initialized.
This is usually the case, but in the Node Routepart Handler it is not.
We need to do some further investigation to see if FLOW3 could provide the necessary information already at that early stage.
Maybe, isVisible() should only tell if the Node has any visibility modifiers set and access restrictions should be handled separately.