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/di.js

@@ -5,7 +5,8 @@
  * The `di` module provides dependency injection container services.
  */
 
-export {Inject, InjectPromise, InjectLazy, Injectable, Optional, DependencyAnnotation} from './src/di/annotations';
+export * from './src/di/annotations';
+export * from './src/di/decorators';
 export {Injector} from './src/di/injector';
 export {Binding, ResolvedBinding, Dependency, bind} from './src/di/binding';
 export {Key, KeyRegistry} from './src/di/key';