title: X-axis category name from string in series list
body: <p>Is it possible to get the x-axis names from a string in my series list? I'm building this series list on the backend and would like to use the "New York", "LA" and "Chicago" as my x-axis category values.</p>
  
  <p>I would expect "New York", "LA" and "Chicago" as my x-axis labels, however, I'm getting -0.25 through 2.25.</p>
  
  <p>Thanks.</p>
  
  <p><a href="http://jsfiddle.net/nicholasduffy/H7zgb/2/" rel="noreferrer">http://jsfiddle.net/nicholasduffy/H7zgb/2/</a></p>
  
  <pre><code>$(function () {
  var chart = new Highcharts.Chart({
      chart: {
          renderTo: 'container',
          type: 'column'
      },
      plotOptions: {
          column: {
              stacking: 'normal',
              dataLabels: {
                  enabled: false
              }
          }
      },
      series: [{
          "data": [
              ["New York", 3570.5],
              ["LA", 50128.38],
              ["Chicago", 5281.22]
          ],
          "name": "Stuff"
      }, {
          "data": [
              ["New York", 10140.84],
              ["LA", 21445.04],
              ["Chicago", 12957.77]
          ],
          "name": "Junk"
      }, {
          "data": [
              ["New York", 65119.6],
              ["LA", 103118.6],
              ["Chicago", 78349.6]
          ],
          "name": "Other Stuff"
      }]
  });
  </code></pre>
  
  <p>});</p>