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/test/forms/integration_spec.js

@@ -14,7 +14,7 @@ import {
 } from 'angular2/test_lib';
 import {DOM} from 'angular2/src/dom/dom_adapter';
 
-import {Inject} from 'angular2/di';
+import {Inject} from 'angular2/src/di/annotations_impl';
 
 import {Component, Directive} from 'angular2/src/core/annotations_impl/annotations';
 import {View} from 'angular2/src/core/annotations_impl/view';