public HistoryModel(ValueModel parent)
 {
     this.parent = parent;
 }
 /// <summary>
 /// Converts model into html 
 /// </summary>
 /// <param name="helper"></param>
 /// <param name="model"></param>
 /// <returns>Html for illustration model on the page, not for editig.</returns>
 public static MvcHtmlString RenderModel(this HtmlHelper helper, ValueModel model)
 {
     return helper.RenderValue(model.Value, model.Type);
 }