title: How to use ExpandAll and CollapseAll For Grouping Grid using grouping feature
body: <p>I am trying to use expandAll() and collapseAll() for a grouping grid Ext 4.1</p>
  
  <p>But its not working after overriding:
  getting errors expandAll() is not defined</p>
  
  <pre><code>            Ext.override(Ext.grid.feature.Grouping, {
                    collapseAll: function() {
                      var self = this, view = self.view;
                      view.el.query(self.eventSelector).forEach(function (group) {
                        var group_body = Ext.fly(group.nextSibling, '_grouping');
                        self.collapse(group_body);
                      });
                    },
  
                    expandAll: function() {
                      var self = this, view = self.view;
                      view.el.query(self.eventSelector).forEach(function (group) {
                        var group_body = Ext.fly(group.nextSibling, '_grouping');
                        self.expand(group_body);
                      });
                    }
                  });
  </code></pre>
  
  <p>Here is my view file: </p>
  
  <pre><code> Ext.define('MCT.view.MyGrid',
     {
       extend:'Ext.grid.Panel',
       initComponent:function(){
         var me  = this;
         this.bbar = [{xtype:'button',text:'Expand All', handler:function(){
  
            me.features[0].expandAll();
  
            this.callParent(arguments);
  
  
          }}];
       },
       features : [{
          ftype : 'grouping',
                      groupHeaderTpl :'.......',
                      startCollapsed : true
         }]
  
    });
  </code></pre>
  
  <p>Thanks in advance for your help!!</p>