Replace sync onDone callback with SyncProgressListener

[Sitaram Pavan Kumar Kalluri]

Is your feature request related to a problem? Please describe.

The sync method which accepts onDone function as a callback to notify the sync completion is deprecated. From now, the sync progress will be notified via the SyncProgressListener.

Following are the files which has onDone usage:

• lib/services/backend_service.dart

Describe the solution you'd like

• Refactor the code to remove the usage of onDone callback in the above-mentioned files and use SyncProgressListener to be notified on the sync progress.

The sample code can be found here: sync_progress_listener_sample_usage