title: Material-ui & TouchTap: Getting key of ListItem
body: <p>I have a list of items using material-ui. I would like to call _handleTouchTap() when the item is clicked and pass the key of the ListItem to the handler.</p>
  
  <p>Adding</p>
  
  <pre><code>onTouchTap={this._handleTouchTap}
  </code></pre>
  
  <p>to  is not working as 'this' seems the be the wrong scope</p>
  
  <pre><code>var React = require('react');
  var Mui = require('material-ui');
  var ThemeManager = new Mui.Styles.ThemeManager();
  ThemeManager.setTheme(ThemeManager.types.LIGHT);
  var injectTapEventPlugin = require('react-tap-event-plugin');
  injectTapEventPlugin();
  var List = Mui.List
  var ListItem = Mui.ListItem
  
  var Main = React.createClass({
    childContextTypes: {
      muiTheme: React.PropTypes.object
    },
    getChildContext: function () {
      return {
        muiTheme: ThemeManager.getCurrentTheme()
      }
    },
    render: function() {
      var items = [
        {id: 1, title: 'Item 1'},
        {id: 2, title: 'Item 2'},
        {id: 3, title: 'Item 3'}
      ]
      return (
          &lt;List&gt;
            {items.map(function(item){
              return &lt;ListItem key={item.id} primaryText={item.title} /&gt;
            })}
          &lt;/List&gt;
      )
    },
  
    _handleTouchTap: function() {
      // the key of the item should be passed though here
    }
  });
  
  React.render(&lt;Main /&gt;, document.body);
  </code></pre>