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/src/core/zone/ng_zone.ts

@@ -113,13 +113,13 @@ export class NgZone {
   _onErrorHandler: ErrorHandlingFn;
 
   /** @internal */
-  _onTurnStartEvents: EventEmitter;
+  _onTurnStartEvents: EventEmitter<any>;
   /** @internal */
-  _onTurnDoneEvents: EventEmitter;
+  _onTurnDoneEvents: EventEmitter<any>;
   /** @internal */
-  _onEventDoneEvents: EventEmitter;
+  _onEventDoneEvents: EventEmitter<any>;
   /** @internal */
-  _onErrorEvents: EventEmitter;
+  _onErrorEvents: EventEmitter<any>;
 
   // Number of microtasks pending from _innerZone (& descendants)
   /** @internal */