feat(LazyMapsAPILoader): provide shortcut

[sebholstein]

Now, you can use a shortcut to configure the LazyMapsAPILoader:

Before:

bootstrap(AppComponent, [
  ANGULAR2_GOOGLE_MAPS_PROVIDERS,
  provide(LazyMapsAPILoaderConfig, {useFactory: () => {
    let config = new LazyMapsAPILoaderConfig();
    config.apiKey = 'mykey';
    return config;
  }})
])

After:

import {provide} from 'angular2/core';
import {provideLazyMapsAPILoaderConfig} from
'angular2-google-maps/core';

bootstrap(AppComponent, [
  GOOGLE_MAPS_PROVIDERS,
  provideLazyMapsAPILoaderConfig({ apiKey: 'myKey' })
])

Closes #388