feat(browser): use AppModules for bootstrap in the browser

This introduces the `BrowserModule` to be used for long form
bootstrap and offline compile bootstrap:

```
@AppModule({
  modules: [BrowserModule],
  precompile: [MainComponent],
  providers: […], // additional providers
  directives: […], // additional platform directives
  pipes: […] // additional platform pipes
})
class MyModule {
  constructor(appRef: ApplicationRef) {
    appRef.bootstrap(MainComponent);
  }
}

// offline compile
import {bootstrapModuleFactory} from ‘@angular/platform-browser’;
bootstrapModuleFactory(MyModuleNgFactory);

// runtime compile long form
import {bootstrapModule} from ‘@angular/platform-browser-dynamic’;
bootstrapModule(MyModule);
```

The short form, `bootstrap(...)`, can now creates a module on the fly,
given `directives`, `pipes, `providers`, `precompile` and `modules`
properties.

Related changes:
- make `SanitizationService`, `SecurityContext` public in `@angular/core` so that the offline compiler can resolve the token
- move `AnimationDriver` to `platform-browser` and make it
  public so that the offline compiler can resolve the token

BREAKING CHANGES:
- short form bootstrap does no longer allow
  to inject compiler internals (i.e. everything 
  from `@angular/compiler). Inject `Compiler` instead.
  To provide custom providers for the compiler,
  create a custom compiler via `browserCompiler({providers: [...]})`
  and pass that into the `bootstrap` method.

modules/@angular/core/core.dart

@@ -7,7 +7,7 @@ export './src/core/di.dart' hide ForwardRefFn, resolveForwardRef, forwardRef;
 export './src/facade/facade.dart';
 export './src/core/application_ref.dart' show createPlatform, assertPlatform,
     disposePlatform, getPlatform,
-    coreLoadAndBootstrap, coreBootstrap, createNgZone, PlatformRef, ApplicationRef;
+    coreLoadAndBootstrap, coreBootstrap, PlatformRef, ApplicationRef;
 export './src/core/application_tokens.dart' show APP_ID,
   APP_INITIALIZER,
   PACKAGE_ROOT_URL,