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....
We need to file a bug on this. OPTIONS is a completely legit method and has uses in other places (like detecting WebDAV compliance). So in an ideal world we really need to let it go and just append the cors headers on the way back. But that is certainly a pri 3. So just filing a bug and moving on is fine.