Review changes

[mcottontensor]

• Tidied up the tsc build process of the common library
• Added WebSocketsTransportNJS implementation to common library for use with node.js applications using this lib.
• Fixed issue with offer/answer handling in frontend lib. This was still working due to the way messages get constructed but the code was still incorrect.
• Adding some comments to SignallingProtocol to explain what events are fired on what emitter
• Moved SignallingProtocol from the WebSockets folder to the Protocol folder since it has nothing to do with websockets now.
• Altered the signaling tester docker to use code in repo rather than published packages.

[lukehb]

PR itself looks great. As discussed, the failing test should use npm link instead of remote dependency, so it is testing latest source.