Mock a the minimal subset of WebRTC for testing.

The intent of this PR is to introduce a basic mocking of the WebRTC API. Just enough to make [shortwave](inetCatapult/shortwave) work with Zombie.js integration tests.

I am going to be adding tests to this PR.
Would it not be simpler to use class hierarchies to your advantage rather than creating common state on the global scope and then calling a class method to consume that state?