Add support for username+password from the URL

[hgfischer]

No description provided.

[mobz]

@hgfischer I've reviewed your patch. I think it would be preferable if the user/pass was more integrated into the way user/pass can be transferred as a url param of head, so that both mechanisms end up effecting the same control structure.

for example putting ?auth_user=foo in the browsers location bar adds Authorisation header via $.ajaxSetup. It would be good if they worked the same way. app.js around line 13 might be the right place for this.

I noticed also that you add call['xhrFields'] = { withCredentials: true }; which might be more generally useful as well.