Provide a way to disable app data cloud backup

### Problem description

Currently, on Android, one can disable cloud backup by setting AndroidManifest.xml application's attribute `android:allowBackup` to `"false"` (see https://developer.android.com/guide/topics/data/autobackup#EnablingAutoBackup) by including the following in config.xml:

```




```

On iOS, the `localStorage` implementation is based on a Documents file, which is automatically backed up (see https://developer.apple.com/icloud/documentation/data-storage/index.html) and this behavior cannot be configured.

### Expected behavior

Tabris.js should provide API to disable backup for app storages on iOS. See [native API](https://developer.apple.com/library/archive/qa/qa1719/_index.html).