Progress bars for uploading at end of training run

[bfirsh]

Why

When training has finished, there may be files left to upload in the background. This currently displays an message saying "Replicate is still uploading..." but this will just hang for ages if there are large files.

How

It would be much better if this displayed constant progress to the user. If it's an interactive terminal, display progress bars. If it's a non-TTY log file, display something useful and not too verbose line-by-line.

Related

#316

This is a follow-on of #408