Replace previous callback based basic client with an easier
to use object-oriented API that further abstracts the low level
details of the WebSockets Server surface messaging protocol.
All built-in web surface demos were updated to use the new API.
add methods to callback.js
automatically reconnect js client on disconnection
mixer-demo do not recreate UI on reconnection
NO-OP: indentation in message.js
make client JS reconnection optional
fix mixer-demo scrolling
minor JS client refactor
improve mixer-demo readability