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.
Since JavaScript does not have an enumerator type, what does this buy us? Do we expect that `STATE.new` will ever evaluate to something other than "new"? I would think that we would rename the property in that case.