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/examples/src/material/demo_common.js

@@ -2,7 +2,7 @@ import {IMPLEMENTS, print} from 'angular2/src/facade/lang';
 import {UrlResolver} from 'angular2/src/services/url_resolver';
 import {isPresent, isBlank, RegExpWrapper, StringWrapper, BaseException} from 'angular2/src/facade/lang';
 import {DOM} from 'angular2/src/dom/dom_adapter';
-import {Injectable} from 'angular2/di';
+import {Injectable} from 'angular2/src/di/annotations_impl';
 import {ReflectionCapabilities} from 'angular2/src/reflection/reflection_capabilities';
 import {reflector} from 'angular2/src/reflection/reflection';
 import {BrowserDomAdapter} from 'angular2/src/dom/browser_adapter';