refactor(core): support non reflective bootstrap.

This changes Angular so that it can be used without reflection (assuming a codegen for injectors).

BREAKIKNG CHANGE:
- Drops `APP_COMPONENT` provider. Instead, inject
  `ApplicationRef` and read its `componentTypes` property.
- long form bootstrap has changed into the following:
  ```
  var platform = createPlatform(ReflectiveInjector.resolveAndCreate(BROWSER_PROVIDERS));
  var appInjector =
    ReflectiveInjector.resolveAndCreate([BROWSER_APP_PROVIDERS, appProviders], platform.injector);
  coreLoadAndBootstrap(appInjector, MyApp);
  ```

modules_dart/angular2_testing/lib/angular2_testing.dart

@@ -4,7 +4,7 @@ import 'package:test/test.dart';
 
 import 'package:angular2/angular2.dart';
 import 'package:angular2/src/core/di/metadata.dart' show InjectMetadata;
-import 'package:angular2/src/core/di/exceptions.dart' show NoAnnotationError;
+import 'package:angular2/src/core/di/reflective_exceptions.dart' show NoAnnotationError;
 import 'package:angular2/src/core/reflection/reflection.dart';
 import 'package:angular2/src/core/reflection/reflection_capabilities.dart';
 import 'package:angular2/src/testing/test_injector.dart';