WebWolf: add a page to create a response

[nbaars]

Some lessons need WebWolf to return a response. We now do that with the file-upload option.
It would be nice to have a page to create a response:

URL: http://localhost:9090/<> (adjustable)
Header: text box where each line is a header line
Body: text box for the response.

Buttons: Save, Access log

Access log will give an overview when the endpoint is invoked
The overview page would show each hosted response and an option to go back to the detail screen.