feat(core): Add a long-form syntax for Angular bootstrapping.

This change adds a syntax for bootstrapping Angular on a page that allows more fine-grained control of the hierarchy created. platform() creates a platform injector (of which there can only be one). From the platform, .application() creates an Angular application including a Zone and all specified application bindings (e.g. for the DOM, HTTP, Compiler, Renderer, etc). At the application level, .bootstrap() will bootstrap the given component into that application.

Closes #3852

modules/angular2/src/core/bootstrap.dart

@@ -2,7 +2,7 @@ library angular2.src.core.bootstrap;
 
 import 'dart:async';
 
-import 'application_ref.dart';
+import 'package:angular2/src/core/compiler/dynamic_component_loader.dart' show ComponentRef;
 import 'package:angular2/src/core/reflection/reflection.dart' show reflector;
 import 'package:angular2/src/core/reflection/reflection_capabilities.dart'
     show ReflectionCapabilities;
@@ -14,7 +14,7 @@ import 'application_common.dart';
 /// mirrors and produces a faster and more compact JS code.
 ///
 /// See [commonBootstrap] for detailed documentation.
-Future<ApplicationRef> bootstrap(Type appComponentType,
+Future<ComponentRef> bootstrap(Type appComponentType,
     [List componentInjectableBindings]) {
   reflector.reflectionCapabilities = new ReflectionCapabilities();
   return commonBootstrap(appComponentType, componentInjectableBindings);