Relay prototype

Considering getting this simple relay implementation into ThaliProject while I finish up the other aspects of it - to simplify folks using the HTML5 seed.   Perhaps into a new branch on ThaliProject - but then you wouldn't be able to see the diff for review.

Only one source file here for the relay - RelayWebServer.java (and RelayWebServerTest.java).  The other bits are all NanoHTTPD.  Open questions on code file headers for those....
I don't think IPv4 will ever be a problem in the sense you mean. As for security considerations, CORS isn't a problem because we will be adding the shared secret support to the proxy so any request without the right secret will be rejected without CORS.