Use NavController as the public API, and NavControllerBase as the
internal API. Refactored all app/nav/tabs unit tests and created
centralized mocking functions.
BREAKING CHANGES:
- Ionic's custom decorators have been removed.
- `@App` and `@Page` should be replaced with `@Component`.
- `IonicApp` has been renamed to `App`.
- `ionicBootstrap` is required to bootstrap the app.
- Config is now the 3rd parameter in `ionicBootstrap(rootComponent,
providers, config)`.
- Property `prodMode` is now a config option, enabling or disabling
production mode.