move to a samples folder hierarchy

One sample app wasn't working for me.

This introduces a samples/ folder under which we can place any number of sample apps. Right now, I've moved the existing "copy paste" app there and added a new one, "turn",  which just spins up a TURN server on localhost:9997 -- I'm finding this very useful for testing TURN functionality in isolation. Copy and pasting all the time is too slow!

Next step will be to add another sample app which uses a *transport provider*. That will be an *obfuscating* transport provider which consumers of this repo, e.g. socks-rtc, will use.