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/native-audio/index.ts

@@ -36,7 +36,9 @@ import { Cordova, IonicNativePlugin, Plugin } from '@ionic-native/core';
   repo: 'https://github.com/floatinghotpot/cordova-plugin-nativeaudio',
   platforms: ['Android', 'Browser', 'iOS']
 })
-@Injectable()
+@Injectable({
+  providedIn: 'root'
+})
 export class NativeAudio extends IonicNativePlugin {
   /**
    * Loads an audio file into memory. Optimized for short clips / single shots (up to five seconds). Cannot be stopped / looped.