refactor(async): refactor EventEmitter

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`

modules/angular2/test/core/forms/integration_spec.ts

@@ -907,7 +907,7 @@ class WrappedValue implements ControlValueAccessor {
 
 @Component({selector: "my-input", template: ''})
 class MyInput implements ControlValueAccessor {
-  @Output('change') onChange: EventEmitter = new EventEmitter();
+  @Output('change') onChange: EventEmitter<any> = new EventEmitter();
   value: string;
 
   constructor(cd: NgControl) { cd.valueAccessor = this; }

modules/angular2/test/core/forms/model_spec.ts

@@ -133,7 +133,7 @@ export function main() {
         if (!IS_DART) {
           it("should update set errors and status before emitting an event",
              inject([AsyncTestCompleter], (async) => {
-               c.valueChanges.toRx().subscribe(value => {
+               c.valueChanges.subscribe(value => {
                  expect(c.valid).toEqual(false);
                  expect(c.errors).toEqual({"required": true});
                  async.done();