title: Displaying the number of rows in footer of webix grid
body: <p>Is there an easy way to display the number of DataTable rows in its footer? I've found <a href="http://docs.webix.com/samples/15_datatable/12_header_footer/06_counter.html" rel="nofollow">the demo</a> with the counter in the footer with a summColumn function, but I can't find the function for counting rows.</p>