code: public JQMListItem addItem(String text, String url,
                                 ListItemImageKind imageKind, String imageUrl) {
          return addItem(items.size(), text, url, imageKind, imageUrl);
      }
docs: This method is needed as good enough workaround for the following issue:
  <a href="https://github.com/sksamuel/jqm4gwt/issues/18">List item with icon/thumbnail</a>
  
  @param url - could be null in case of non-clickable/readonly item. Empty string means
  it will be clickable!
  
  @param imageUrl - could be null/empty initially, and then set later manually
  (but imageKind must not be NONE if you are planning to set images for this item).