public ActionResult List()
        {
            var tags                = _postService.Tags();
            var categories          = _postService.Categories();
            CategoriesTagsList list = new CategoriesTagsList();

            list.Categories = categories;
            list.Tags       = tags;
            return(View("List", list));
        }
        /// <summary>
        /// Return collection of categories.
        /// </summary>
        /// <returns></returns>

        public ActionResult Categories()
        {
            var viewModel = _postService.Categories();

            return(PartialView("_Categories", viewModel));
        }