Add test for Node environment

[mattzeunert]

We need to check the library loads without issues in a Node environment, and that it's possible to create a breakpoint.

(Not all breakpoints will work because some rely on the DOM. They're still in the NPM version, but I don't think it's a problem for now.)

This is the code I was using before for manual testing. We'd need a second Karma environment to run the Node tests in.

var bps = require("./extension/build/javascript-breakpoint-collection.js")
var obj = {greeting: "hi"}
bps.debugPropertySet(obj, "greeting", "trace")
obj.greeting = "hello"

(The main thing that could go wrong without tests is that we accidentally try to access window or document in shared code, since those global variables don't exist in a Node env.)