CB-8095 Adds support for progress events to upload operation

This fixes [CB-8095](https://issues.apache.org/jira/browse/CB-8095)

On windows FileTrasfer doesn't support progress events for upload operation properly since internal implementation uses XHR which doesn't provide all information, necessary to fire correct progress events.

This PR replaces XHR with `BackgroundUploader` class which itself supports progress notification in more convenient way and can provide all necessary data for progress events for FileTransfer.