webui: improve rule table css
    
    - category radio line has line-height large enough to contain
      undo button -> content doesn't move several pixels on change
    - remove vertical padding from btns in table headers to maintain
      about the same height
    - remove invisible border from link buttons to have the same height
      for disabled and enabled button
    
    Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>