title: Highcharts: when exporting, unselected series should not show in the legend
body: <p>In highcharts, series can be selected/unselected by clicking on their names in the legend.
  If I have some series unselected (they are greyed in the legend), the export function will create an image where the unselected series name are visible.</p>
  
  <p>How can I make the unselected series names <strong>not visible in the legend</strong> when I export them to a graphic?</p>