private void CmdFolderAdd(object sender, ExecutedRoutedEventArgs e) {
   FolderBrowserDialog dir = new FolderBrowserDialog();
   if (dir.ShowDialog() == DialogResult.OK) {
     var path = $"{dir.SelectedPath}{(dir.SelectedPath.EndsWith("\\") ? string.Empty : "\\")}";
     if (!Paths.Contains(path)) {
       Paths.Add(path);
       LoadFolders();
     }
   }
 }