title: Change the icon of a jQuery UI button with own image
body: <p>Currently I have the following jQuery UI button:</p>
  
  <pre><code>$('#button').button(
    {
      label: 'Test',
      icons: {primary: 'ui-icon-circle-plus', secondary: null}
    }
  );
  </code></pre>
  
  <p>I wish to use own image for the button called 'custom.png'.</p>
  
  <p>How I can achieve that?</p>