private void MenuItemsListView_ItemClick(object sender, ItemClickEventArgs e)
        {
            var menuItem = (MenuItem)e.ClickedItem;

            CategoryTextBlock.Text = menuItem.Category.ToString();
            PictureManager.GetPicturesByCategory(pictures, menuItem.Category);
            BackButton.Visibility = Visibility.Visible;

            //Picture menuItem = (Picture)e.ClickedItem;
            //CategoryTextBlock.Text = menuItem.Category.ToString();
            //PictureManager.GetPicturesByCategory(pictures, menuItem.Category);
            //BackButton.Visibility = Visibility.Visible;
        }