showDialog(type, ui, msg) {
    _ui.showDialog(type, ui, msg);
  }
Show a pop-over "toast" dialog or a modal alert
Refs: https://www.w3.org/WAI/ARIA/apg/example-index/dialog-modal/alertdialog.html,
      https://www.w3.org/WAI/ARIA/apg/example-index/dialog-modal/dialog.html,
      https://www.w3.org/WAI/ARIA/apg/patterns/dialogmodal/
@param {"notify"|"alert"} type Dialog type
@param {object} ui standardised ui data
@param {object} [msg] msg.payload/msg.topic - only used if a string. Optional.
@returns {void}