Added environment info and dependencies

[toddhgardner]

This change exposes the other environment info on payload to be specified. Everything is just on initialize(options) for simplicity. For example:

  TrackJS.initialize({
    token: 'test token',
    transport,
    dependencies: {
      "foo": "1.2.3"
    },
    originalUrl: "original-url",
    referrerUrl: "referrer-url",
    userAgent: userAgent("Node", "12.1", "windows", "x64", "11.2"),
  });

Rather than exposing every part of the userAgent as options, I built and exported a utility to construct the string. That way, if we are operating in a browser-like environment, you can still just set the userAgent string directly.

To do later: Need to figure out how to expose the agent version as a variable. Need to add some sort of build-step that is more than just typescript compile.