_private: New NS to bunch up stuff that has to be exposed to other parts...

... of the library

_handleHashChange and _registerInternalEvents do not need to be exposed at all, because they are internal to jquery.mobile.navigation.js. Nevertheless, there's a plugin (splitview) that uses _registerInternalEvents (https://github.com/jquery/jquery-mobile/issues/4984) so we should probably keep exposing it as private, at least until we also implement the ability to work with multiple page containers, presumably rendering the plugin obsolete. I'm not sure if _handleHashChange could be un-exposed. We can try it and see if it causes an uproar.