MemberAdminWindow+DeliveryAdminWindow: Add button to jumpt to member (predecessor)

Elwig/App.xaml.cs

@@ -248,5 +248,11 @@ namespace Elwig {
         public static ChartWindow FocusChartWindow(int year, int avnr) {
             return FocusWindow<ChartWindow>(() => new(year, avnr), w => w.Year == year && w.AvNr == avnr);
         }
+
+        public static MemberAdminWindow FocusMember(int mgnr) {
+            var w = FocusWindow<MemberAdminWindow>(() => new());
+            w.FocusMember(mgnr);
+            return w;
+        }
     }
 }