webui: ListViewWidget
    
    A widget for rendering a list of groups of items. Intended to be
    used in sidebar. Plan is to serve also as a base for FacetGroupsWidget.
    
    https://fedorahosted.org/freeipa/ticket/3129
    
    Reviewed-By: Martin Kosek <mkosek@redhat.com>
    Reviewed-By: Tomas Babej <tbabej@redhat.com>