Windows: Prettify formatting for numbers

Elwig/Windows/MailWindow.xaml.cs

@@ -730,7 +730,7 @@ namespace Elwig.Windows {
                 client = await Utils.GetSmtpClient();
                 Mouse.OverrideCursor = null;
 
-                var res = MessageBox.Show($"Sollen {EmailDocuments.Count} E-Mails verschickt werden?",
+                var res = MessageBox.Show($"Sollen {EmailDocuments.Count:N0} E-Mails verschickt werden?",
                     "Rundschreiben verschicken", MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No);
                 if (res != MessageBoxResult.Yes) {
                     return;