feat(decorators): adds decorator versions of DI annotations.

In 'angular2/di' the symbol:
- Inject is a decorator
- InjectAnnotation is an annotation

Internally one an get a hold of annotations without *Annotations appened
(to make ts2dart work without workarounds) by importing from
'angular2/src/di/annotations_impl' instead of 'angular2/di'. This is
needed only for users that transpile through TS and through ts2dart.

modules/angular2/src/core/application.js

@@ -1,4 +1,4 @@
-import {Injector, bind, OpaqueToken, Optional} from 'angular2/di';
+import {Injector, bind, OpaqueToken} from 'angular2/di';
 import {NumberWrapper, Type, isBlank, isPresent, BaseException,
     assertionsEnabled, print, stringify} from 'angular2/src/facade/lang';
 import {BrowserDomAdapter} from 'angular2/src/dom/browser_adapter';