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/annotations/decorators.dart

@@ -0,0 +1,3 @@
+library angular2.core.decorators;
+
+/* This file is empty because, Dart does not have decorators. */

modules/angular2/src/core/annotations/decorators.es6

@@ -0,0 +1,23 @@
+import {
+  ComponentAnnotation,
+  DirectiveAnnotation
+} from './annotations';
+import {ViewAnnotation} from './view';
+import {AncestorAnnotation, ParentAnnotation} from './visibility';
+import {AttributeAnnotation, QueryAnnotation} from './di';
+import {makeDecorator, makeParamDecorator} from '../../util/decorators';
+
+/* from annotations */
+export var Component = makeDecorator(ComponentAnnotation);
+export var Decorator = makeDecorator(DirectiveAnnotation);
+
+/* from view */
+export var View = makeDecorator(ViewAnnotation);
+
+/* from visibility */
+export var Ancestor = makeParamDecorator(AncestorAnnotation);
+export var Parent = makeParamDecorator(ParentAnnotation);
+
+/* from di */
+export var Attribute = makeParamDecorator(AttributeAnnotation);
+export var Query = makeParamDecorator(QueryAnnotation);