title: Target reference line in combination chart
body: <p>I have a combination chart with same type of values on both left y-axis scale and right y-axis scale. When I add a target reference line using lines and curves at some point on y-axis scale, I see two reference lines one for left y axis and the other for right y axis. Is there any option to display only one reference line according to scale on my left y-axis ? 
  Thanks</p>