Add help buttons to the login stack page
    
    The various login stack plugins (mostly) have description attributes,
    but these are not exposed in the UI.  Add a help button to each row of
    the login stack page that uses bootstrap popovers to display the text.
    
    Signed-off-by: Howard Johnson <merlin@merlinthp.org>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>