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....
Actually it should detect duplicate headers because duplicate headers are ALWAYS legal in HTTP and so I have to assume the test framework will properly merge them following HTTP's explicit rules for how to merge duplicate headers.

I also bet they have an enumerator so you can test all headers and make sure there aren't any extras.