LogWindow.xaml の相互作用ロジック
Inheritance: System.Windows.Window
 private void OnShowLogs(object sender, System.Windows.Input.ExecutedRoutedEventArgs e)
 {
     if (logWindow==null) {
     logWindow = new LogWindow { DataContext=((PeerCastAppViewModel)this.DataContext).Log };
       }
       logWindow.Show();
 }