Logout when leaving translate5 not via logout button doesn't work.

Cleaning the cookie on beforeunload is needed to not interpret 302 redirects' HTML as JSON

But this causes sendBeacon to not send it even when it is deleted only after the sendBeacon call

So the /logout API  cannot destroy the session, bc it has no sessionId.

We must in this case send the sessionID as request param because sendBacon allows no header customization. Easiest is as GET parameter, potentially appearing in auth logs. POST is also possible, lookup the sendBeacon API for it.

Then in the logoutHandler construct the sessionToDestroy from the request param instead of the zfExtended  header.