private async void loginButton_Click(object sender, RoutedEventArgs e)
        {
            SyncClient client = new SyncClient();
            await client.SignIn(emailTextBox.Text, passwordTextBox.Password);

            IEnumerable <Bookmark> bookmarks = await client.GetBookmarks();
        }
        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            SyncClient client = new SyncClient();
            await client.SignIn(null, null);

            IEnumerable <Bookmark> bookmarks = await client.GetBookmarks();
        }