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....
Per https://www.mnot.net/blog/2011/07/11/what_proxies_must_do

"This means that the Connection header and any header it lists MUST be removed, as well as TE, Transfer-Encoding, Keep-Alive, Proxy-Authorization, Proxy-Authentication, Trailer and Upgrade."

So please remove those headers.