title: Add the average line of a serie to a chart
body: <p>I have a series of points that has fast changing values, which makes it very spiky and uneasy to read when zooming out.</p>
  
  <p>I would like to know if there is a way to draw above the already existing series, another one that would represent the average of, for exemple: every 10 points, or every point in a minute?</p>
  
  <p>I've looked into dataGrouping but can't seem to make it work, is that what I'm looking for ?</p>
  
  <p>Thanks for reading.</p>