Azure upload/download pool needs to be using multipart block uploads/downloads

What's the issue?
The initial implementation of the Azure upload pool used the 'PutBlob' API call by design so that we could get things implemented, however, it's currently limited to uploading 256 MiB of data, in the long run we should upgrade to using a multipart uploading implementation for larger than normal blocks (in a similar fashion to how we do with S3). See the remarks section of the documentation for more information.

What's the fix?
Upload larger files using multipart uploads.

Update this size seems to have been changed in the latest version of the SDK (which we're not running yet); either way, the new limit is still not high enough for our needs, so we still need to use multipart uploads.