title: ExtJs Chart, How to get boundary dates from selection mask on 'Time' type axis
body: <p>I have ExtJs 4 Area chart with Time serie. I'd like user to be able to horizontally select part of chart and then obtain higher density data from server adequately. Problem is I can't get boundary dates from selection. I've got:</p>
  
  <pre><code>var chart = Ext.create('Ext.chart.Chart', {
    store: store,
    enableMask: true,
    mask: 'horizontal',
    listeners: {
      select: {
          fn: function(me, selection) {
              console.log(arguments); // selection = Object { height: 218, width: 117, x: 665, y: 123 }
          }
      },
    ...
  </code></pre>
  
  <p>But select listener provides only pixel data. Is there some way to get boundary axis data (e.g. { from: 2013-08-01, to: 2013-08-20 } or some way to unproject pixels to values? I'm desperade I would say it's such a basic thing but can't find solution anywhere. Thanks in advance.</p>