Refactor EventEmitter and Async Facade to match ES7 Observable semantics, properly use RxJS typedefs, make EventEmitter inherit from RxJS Subject. Closes#4149.
BREAKING CHANGE:
- consumers of EventEmitter no longer need to call .toRx()
- EventEmitter is now generic and requires a type - e.g. `EventEmitter<string>`
- EventEmitter and Observable now use the `.subscribe(generatorOrNext, error, complete)` method instead of `.observer(generator)`
- ObservableWrapper uses `callNext/callError/callComplete` instead of `callNext/callThrow/callReturn`
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