Add optional Document Id to Documents

Elwig/Documents/DeliveryNote.cshtml.cs

@@ -15,6 +15,7 @@ namespace Elwig.Documents {
                 $"<tr><th>Zweigstelle</th><td>{d.Branch.Name}</td></tr>" +
                 $"</tbody></table>";
             Text = App.Client.DeliveryNoteText;
+            DocumentId = d.LsNr;
         }
     }
 }