refactor(router): use DI imports from public API

This allows us to create smaller CJS bundles for router,
where the bundle doesn't duplicate code from angular2 core.

modules/angular2/router.ts

@@ -28,7 +28,7 @@ import {RouterOutlet} from './src/router/router_outlet';
 import {RouterLink} from './src/router/router_link';
 import {RouteRegistry} from './src/router/route_registry';
 import {Location} from './src/router/location';
-import {provide, OpaqueToken, Provider} from './core';
+import {provide, OpaqueToken, Provider} from 'angular2/angular2';
 import {CONST_EXPR} from './src/core/facade/lang';
 import {ApplicationRef} from './src/core/application_ref';
 import {BaseException} from 'angular2/src/core/facade/exceptions';