webui: use unique ids for checkboxes
    
    Checkboxes have not used unique ids across the whole UI. It broke checking by clicking on label for later displayed instances. It became serious problem when rcue introduced new checkbox styles with 'label clicking' as default check method.
    
    https://fedorahosted.org/freeipa/ticket/3904
    
    Reviewed-By: Adam Misnyovszki <amisnyov@redhat.com>