WebUI: Change structure of Identity submenu
    
    Previously there were 'User Groups', 'Host Groups' and 'Netgroups'
    separately, now these three items are grouped into one named 'Groups'
    which has sidebar with three items mentioned above.
    
    This change allows us to move ID views into Identity submenu.
    
    https://pagure.io/freeipa/issue/6717
    
    Reviewed-By: Simo Sorce <ssorce@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>