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/web_workers/ui/event_dispatcher.ts

@@ -14,7 +14,7 @@ import {StringMapWrapper} from 'angular2/src/core/facade/collection';
 import {EventEmitter, ObservableWrapper} from 'angular2/src/core/facade/async';
 
 export class EventDispatcher implements RenderEventDispatcher {
-  constructor(private _viewRef: RenderViewRef, private _sink: EventEmitter,
+  constructor(private _viewRef: RenderViewRef, private _sink: EventEmitter<any>,
               private _serializer: Serializer) {}
 
   dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>): boolean {