System.register update

This includes the System.register update corresponding to the new format implemented into Traceur here - https://github.com/google/traceur-compiler/pull/1161.

All tests are passing!
I'm just using the module object itself directly... it does mean the module object is writable. As in the comment, it should be a read-only property through Object.defineProperty.

The reason I can't use a proxy object is because if a module imports `module M from 'm'`, we need to be handing the true module object over.