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....
Using the magic path relayutility/localhttpkey is a sub-optimal choice because it intrudes on the legal database namespace. There are however a few options here.

Option 1 - Use a new method name - I did this in the previous relay. Instead of GET or POST introduce "GIVEMETHEKEY" or whatever. This won't conflict with anything and is trivial to test for.

Option 2 - Use a path that can't be a legal database name. Use something that starts, for example, with _ like _relayutility/localhttpkey.

Option 3 - Try to make this look like a full fledged CouchDB call. This gives me the ickies as it's sure to confuse real Couch clients. I would stick with 1 or 2.

I'm happy btw to accept the PR with the code as is if you at least file a bug on this issue. :)