public async Task<Picture> Add(Picture picture)
        {
            _ctx.Pictures.Add(picture);
            await _ctx.SaveChangesAsync();

            return picture;
        }
        public async Task<HttpResponseMessage> Post([FromBody] string imgString)
        {
            string[] stringData = imgString.Split(new[] {','});
            byte[] byteData = Convert.FromBase64String(stringData[1]);


            var picture = new Picture
            {
                Data = byteData
            };

            Picture result = await _service.Add(picture);

            string url = "api/pictures/" + result.Id;

            return Request.CreateResponse(HttpStatusCode.Created, url);
        }