title: Add moving layer to chart when device is unavailable
body: <p>I'm writing a monitoring tool for crypto-coin miners (specifically for nvidia gpus, ccminer) and would like to show to the user in the charts when the device was unavailable. 
  I already have the code that registers at what DateTime it became available/unavailable.<br>
  I thought about adding another series with it's own Y-axis (range 0-1) that would pop-up in the back, as in this little mockup:
  <img src="https://i.stack.imgur.com/75uGu.jpg" alt="Mockup"></p>
  
  <p>But as you can see, my 2 Y axis(es?) are already used for other values.<br>
  I tried googling for "overlay chart C#", "three axis chart C#", etc.. but nothing usable came up. After searching for a day, I give up and hope that there is someone who can guide me towards the right direction?<br>
  Many thanks in advance!</p>