When using openURLFromButton: we will likely be calling this from a
UIBarButtonItem object, which isn't a descendant of the UIView class.
We return the global navigator because there's no simple way
to determine the class from the bar button item. This is a
trade-off of ease-of-use over proper functionality here. If you want
to get a UIBarButtonItem to open a specific navigator, handle the
button tapped method yourself and get the correct navigator.