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....
Probably... Need to make a clean pass over all of that including the cors behavior once we get a little further as there are security implications all over it.  Does 127.0.0.1 have IPv4 implications that actually matter here ever?  (probably not).