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

BREAKING CHANGE:

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

Closes #4287

Closes #5302

modules/angular2/docs/web_workers/web_workers.md

@@ -230,7 +230,7 @@ import {bootstrap} from 'angular2/web_worker/ui';
 var instance = bootstrap("loader.js");
 var bus = instance.bus;
 bus.initChannel("My Custom Channel");
-bus.to("My Custom Channel").next("hello from the UI");
+bus.to("My Custom Channel").emit("hello from the UI");
 ```
 ```TypeScript
 // background_index.ts, which is running on the WebWorker