ContextWindow: Use Task.Run to load data outside main thread

Elwig/Windows/BaseDataWindow.xaml.cs

@@ -153,7 +153,7 @@ namespace Elwig.Windows {
             ParameterExportEbicsAddress.IsEnabled = true;
         }
 
-        private void Window_Loaded(object sender, RoutedEventArgs evt) {
+        protected override async Task OnInit(AppDbContext ctx) {
             LockInputs();
         }