Allow the RadDateTimePicker editor of RadGridView to allow replacement of the months' popup.

Resolution:   This behavior can be achieved when set the HeaderNavigationMode property to Zoom of RadCalendar. The feature is introduced in Q2 2014.  
For example: 
void radGridView1_CellEditorInitialized(object sender, Telerik.WinControls.UI.GridViewCellEventArgs e)
        {
            RadDateTimeEditor dtEditor = e.ActiveEditor as RadDateTimeEditor;
            if (dtEditor != null)
            {
                RadDateTimeEditorElement element = (RadDateTimeEditorElement)dtEditor.EditorElement;
                element.Calendar.HeaderNavigationMode = HeaderNavigationMode.Zoom;
            }
        }