title: Custom Renderer in Ext-js - Bryntum/ExtJs UTC Date Issue
body: <p>I'm trying to add a <strong>custom renderer</strong> to Bryntum Ext Gantt chart. </p>
  
  <p>I have dates which are being shown in the local timezone, but I wish to show them in the UTC date because this is what the datasource is using to present the user with date (it's agnostic of browser time-zone) in the source application.</p>
  
  <p>The post here led me in the right direction (seems to be what I need based on my tests): <a href="https://stackoverflow.com/questions/9023641/why-does-extjs-subtract-a-day-when-formatting-a-date">Why does ExtJS subtract a day when formatting a date?</a></p>
  
  <p><em>How do I implement linked solution into a custom renderer</em>?</p>
  
  <hr>
  
  <p>I tried this and the column was blank: </p>
  
  <pre><code>{
      xtype:'startdatecolumn',
      sortable: false,
      text: 'Start',
      dataIndex: 'StartDate',
      renderer: function (v, m, r) {
          return Ext.util.Format.date(Ext.Date.parse(v, "Y-m-d"), "m-d-Y");
      }
  }
  </code></pre>
  
  <p>Also tried this and the column was blank: </p>
  
  <pre><code>{
      xtype:'startdatecolumn',
      sortable: false,
      text: 'Start',
      dataIndex: 'StartDate',
      renderer: function (v) {
          var dt = Ext.Date.parse(v, "Y-m-d");
          Ext.util.Format.date(dt, "m-d-Y");
          return dt;
      }
  }
  </code></pre>
  
  <p>With this format, it shows the date in local timezone (incorrect unless set to UTC). </p>
  
  <pre><code>{   
      xtype:'enddatecolumn',
      dataIndex: 'EndDate',
      sortable: false,
      text: 'End'
  }
  </code></pre>
  
  <hr>
  
  <h1>Bryntum Column Example</h1>
  
  <pre><code> columns : [
              {
                  xtype : 'treecolumn',
                  header: 'Tasks',
                  sortable: true,
                  dataIndex: 'Name',
                  width: 200,
                  field: {
                      allowBlank: false
                  },
                  renderer : function(v, meta, r) {
                      if (!r.data.leaf) meta.tdCls = 'sch-gantt-parent-cell';
  
                      return v;
                  }
              },
              {
                  xtype : 'startdatecolumn'
              },
              {
                  //hidden : true,
                  xtype : 'enddatecolumn'
              },
  </code></pre>