private async void lbSessions_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (lbSessions.SelectedItem != null)
            {
                try
                {
                    currentSession         = null;
                    currentScreens         = null;
                    txbCurrentSession.Text = "";
                    lbScreens.ItemsSource  = null;
                    currentSession         = lbSessions.SelectedItem as ExamSession;

                    var res = await RestClient.GetScreenshotFromSession(currentSession.id);

                    currentScreens = JsonConvert.DeserializeObject <ScreenshotSessionData>(res);

                    lbScreens.ItemsSource  = currentScreens.Shots;
                    txbCurrentSession.Text = currentSession.student + " [Status:" + currentSession.status + "]";
                }
                catch (Exception ex)
                {
                    await this.ShowMessageAsync("Error bij lbSessions_SelectionChanged ", "Error=" + ex.Message);
                }
            }
        }
        //public FullImgWindow()
        //{
        //    InitializeComponent();
        //}

        public FullImgWindow(ScreenshotSessionData allscreenin, ExamSession currentSessionin)
        {
            InitializeComponent();
            allScreens     = allscreenin;
            currentSession = currentSessionin;
        }