This is pretty unused and gets in the way of the next steps.
A potential side effect is that for templates the widget was passed as
the user data argument. If that turns out to be important, we have to
special case that situation.
And have a priv->display instead of a priv->screen.
Includes turning gtk_menu_set_screen() into gtk_menu_set_display(),
because that function just forwards to its window.
This only used by luck before. We are changing a property from the
::notify handler for that property. Now that GtkRevealer is notifying
the property when it stops animations on unmap, we end up in a life
lock situation where we never make it out of the notify queue.
Fix this by not restarting the animation if the widget is unmapped.
