We need to return the URL as a header in AJAX request for logging

[Huw Wilkins]

As part of an AJAX log of times we would like to include the URL. It seems the only way to get this URL is to return it as a x-header.

Can we add a new header? Something like: X-LP-URL

I think we should return this on all AJAX requests. Lifeless helpfully adds: "api requests on non api domains are ajax requests" if that helps in determining when to add this header.