Spike: Transpile to System.register

Alternative to #120. See discussion first.

Depends on [systemjs](https://github.com/systemjs/systemjs)'s [`System.register` shim](https://github.com/systemjs/systemjs/blob/master/lib/system-register.js).

* [ ] Deal with anonymous module names where `this.moduleName` is undefined
* [ ] 10% Complete test suite

/cc @guybedford @domenic @stefanpenner @caridy @wycats