Add support for multi-file and folder opening

Selecting multiple files and folders, then
pressing enter now opens them in the following
manner:
- Single selection
  - Open file in respective application (existing)
  - Navigate to folder in current tab (existing)
- Multi-selection
  - Open files in respective applications
  - Open folders in a new tab each

Author: jeffsieu

Files UWP/GenericFileBrowser.xaml.cs

@@ -335,7 +335,7 @@ private void AllView_PreviewKeyDown(object sender, KeyRoutedEventArgs e)
         {
             if (e.Key == VirtualKey.Enter)
             {
-                tabInstance.instanceInteraction.OpenItem_Click(null, null);
+                tabInstance.instanceInteraction.List_ItemClick(null, null);
                 e.Handled = true;
             }
         }