code: public DialogButton setIcons(UiIcon primary, UiIcon secondary)
  	{
  		options.put("icons", new ButtonIcon(primary, secondary));
  		return this;
  	}
docs: * Icons to display, with or without text (see text option). The primary icon is
  displayed on the left of the label text, the secondary on the right. Value for the
  primary and secondary properties must be a classname (String), eg. "ui-icon-gear".
  For using only a primary icon: icons: {primary:'ui-icon-locked'}. For using both
  primary and secondary icon: icons:
  {primary:'ui-icon-gear',secondary:'ui-icon-triangle-1-s'}
  
  @param primary
  The primary icon (should be non-null)
  @param secondary
  The secondary icon (might be null).
  @return the button