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_impl/annotations.js

@@ -1,6 +1,6 @@
 import {CONST, normalizeBlank, isPresent} from 'angular2/src/facade/lang';
 import {ListWrapper, List} from 'angular2/src/facade/collection';
-import {Injectable} from 'angular2/di';
+import {Injectable} from 'angular2/src/di/annotations_impl';
 import {DEFAULT} from 'angular2/change_detection';
 
 // type StringMap = {[idx: string]: string};

modules/angular2/src/core/annotations_impl/di.js

@@ -1,5 +1,5 @@
 import {CONST} from 'angular2/src/facade/lang';
-import {DependencyAnnotation} from 'angular2/di';
+import {DependencyAnnotation} from 'angular2/src/di/annotations_impl';
 
 /**
  * Specifies that a constant attribute value should be injected.

modules/angular2/src/core/annotations_impl/visibility.js

@@ -1,5 +1,5 @@
 import {CONST} from 'angular2/src/facade/lang';
-import {DependencyAnnotation} from 'angular2/di';
+import {DependencyAnnotation} from 'angular2/src/di/annotations_impl';
 
 /**
  * Specifies that an injector should retrieve a dependency from the direct parent.