Safeguard on `delete` button in workflow builder.

[VGPReys]

It is in my opinion too easy to delete a module with the Delete button in workflow builder.

I believe that having a are you sure you want to delete the module: Yes/No popup would make it more safe.

[sverhoeven]

Or instead of having a delete prompt, it might be nice to have a undo/redo stack. Where you can rollback the deletion with CTRL-Z or Command-Z