public static void AddFunction(string function, string description)
        {
            var func = FilterFunction.FirstOrDefault(f => f.Text == function);

            if (func != null)
            {
                func.Value = description;
            }
            else
            {
                FilterFunction.Add(new SelectListItem {
                    Value = description, Text = function
                });
            }
            // сохранить настройки
            SiteSettings.Instance.FunctionSettings.Functions = FilterFunction.Select(i => new TraderFilterFunction(i)).ToList();
            SiteSettings.Instance.SaveSettings();
        }
        public static void DeleteFunction(string function)
        {
            if (FilterFunction.Count <= 1)
            {
                return;
            }

            var func = FilterFunction.FirstOrDefault(f => f.Text == function);

            if (func == null)
            {
                return;
            }
            FilterFunction.Remove(func);

            // сохранить настройки
            SiteSettings.Instance.FunctionSettings.Functions = FilterFunction.Select(i => new TraderFilterFunction(i)).ToList();
            SiteSettings.Instance.SaveSettings();
        }