refactor(core): Introduce AppInitStatus

This class allows any provider to know and wait for the initialization of the
application. This functionality previously was tied to `ApplicationRef`.

BREAKING CHANGE:
- `ApplicationRef.waitForAsyncInitializers` is deprecated. Use 
  `AppInitStatus.donePromise` / `AppInitStatus.done` instead.

modules/@angular/core/src/application_module.ts

@@ -8,6 +8,7 @@
 
 import {Type} from '../src/facade/lang';
 
+import {AppInitStatus} from './application_init';
 import {ApplicationRef, ApplicationRef_, isDevMode} from './application_ref';
 import {APP_ID_RANDOM_PROVIDER} from './application_tokens';
 import {IterableDiffers, KeyValueDiffers, defaultIterableDiffers, defaultKeyValueDiffers} from './change_detection/change_detection';
@@ -44,6 +45,7 @@ export const APPLICATION_COMMON_PROVIDERS: Array<Type|{[k: string]: any}|any[]>
   providers: [
     ApplicationRef_,
     {provide: ApplicationRef, useExisting: ApplicationRef_},
+    AppInitStatus,
     Compiler,
     {provide: ComponentResolver, useExisting: Compiler},
     APP_ID_RANDOM_PROVIDER,