WebSocket-Resources / websocket refactor

This commit provides the javascript complement to
[WebSocket-Resources](https://github.com/WhisperSystems/WebSocket-Resources),
allowing us to use a bi-directional request-response framework over
websockets.

See websocket-resources.js and websocket-resources_test.js
for usage details.

Along the way I also factored the websocket keepalive and reconnect
logic into its own file/wrapper object.