refactor(EventEmitter): rename .next() to .emit()

BREAKING CHANGE:

EventEmitter#next(value) is deprecated, use EventEmitter#emit(value)
instead.

Closes #4287

Closes #5302

modules/angular2/test/core/testability/testability_spec.ts

@@ -34,9 +34,9 @@ class MockNgZone extends NgZone {
     this._onEventDoneStream = new EventEmitter(false);
   }
 
-  start(): void { ObservableWrapper.callNext(this._onTurnStartStream, null); }
+  start(): void { ObservableWrapper.callEmit(this._onTurnStartStream, null); }
 
-  finish(): void { ObservableWrapper.callNext(this._onEventDoneStream, null); }
+  finish(): void { ObservableWrapper.callEmit(this._onEventDoneStream, null); }
 }
 
 export function main() {