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/app-preferences/index.ts

@@ -35,7 +35,9 @@ import { Injectable } from '@angular/core';
     'Windows Phone'
   ]
 })
-@Injectable()
+@Injectable({
+  providedIn: 'root'
+})
 export class AppPreferences extends IonicNativePlugin {
   /**
    * Get a preference value