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/testability/testability.js

@@ -1,4 +1,4 @@
-import {Injectable} from 'angular2/di';
+import {Injectable} from 'angular2/src/di/annotations_impl';
 import {DOM} from 'angular2/src/dom/dom_adapter';
 import {Map, MapWrapper, List, ListWrapper} from 'angular2/src/facade/collection';
 import {StringWrapper, isBlank, BaseException} from 'angular2/src/facade/lang';