title: HighStock: One navigator to control two xAxis?
body: <p>I have created two xAxis one at top and another at bottom (with opposite: true) in my highstock chart. But the problem is that navigator is controlling only the bottom xAxis. Changing the navigator only affects the bottom xAxis not the top one. 
  Can we control two xAxis with one navigator in highstock?</p>
  
  <p>Here is my sample code:</p>
  
  <pre><code>navigator: {
      xAxis: {
          type: datetime
      }
  },
  
  xAxis: [{
      type: datetime,
  }, {
      type: datetime,
      opposite: true
  }]
  </code></pre>