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/clevertap/index.ts

@@ -23,7 +23,9 @@ declare var clevertap: any;
   repo: 'https://github.com/CleverTap/clevertap-cordova',
   platforms: ['Android', 'iOS']
 })
-@Injectable()
+@Injectable({
+  providedIn: 'root'
+})
 export class CleverTap extends IonicNativePlugin {
   /**
    * notify device ready