refactor: optimize plugins for angular treeshaking

BREAKING CHANGE: You can remove the plugin import from the app.module.ts because of the changed Inject decorator

src/@ionic-native/plugins/firebase/index.ts

@@ -34,7 +34,9 @@ import { Observable } from 'rxjs';
   repo: 'https://github.com/arnesson/cordova-plugin-firebase',
   platforms: ['Android', 'iOS']
 })
-@Injectable()
+@Injectable({
+  providedIn: 'root'
+})
 export class Firebase extends IonicNativePlugin {
   /**
    * Get the device token