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/linker/query_list.ts

@@ -31,7 +31,7 @@ export class QueryList<T> {
   private _results: Array<T> = [];
   private _emitter = new EventEmitter();
 
-  get changes(): Observable { return this._emitter; }
+  get changes(): Observable<any> { return this._emitter; }
   get length(): number { return this._results.length; }
   get first(): T { return ListWrapper.first(this._results); }
   get last(): T { return ListWrapper.last(this._results); }