Enhancements for embedded use cases

I'd like to make three enhancements to ember-twiddle, that open up some interesting use cases for embedding twiddles into a larger app (i.e., for tutorial purposes).

Before I set out to make these changes, I would love some feedback about whether this is a desirable direction to go in.

1. make the "live reload" and "run tests" checkboxes queryParam driven
2. allow the twiddle (the running app) to communicate with the app embedding the twiddle via `postMessage`
3. additionally, send information about tests passing/failing to the app embedding the twiddle, via `postMessage`. I have a qunit addon that already does the bulk of the work https://github.com/mike-north/qunit-events