[webappsec] updated draft SVG: simple CORS request

Jeff Hodges had proposed this diagram previously for the introductory section of CORS.

I've updated it a bit and rebuilt it in a native SVG editor to reduce the size and increase the readability of the raw source.

Comments welcome - if we are happy with this, I'll insert it into a draft along with other changes agreed to previously and we can start a CfC on moving to CR.

Thanks,

-Brad Hill