Fixed navigation problems.
    
    The navigation code has been modified store the facet's state
    separately in the facet object itself. The path state is stored
    in the navigation object. When the path is changed to view a new
    facet, only the path and the state of the new facet will be shown
    in the URL, thus keeping the URL short.
    
    This fixes pagination, bookmark and search filter problems as well.
    
    Ticket #1507, 1516, 1517