Progress indicator during downloads

[abyrd]

I've had the downloads from the FTP server stall a few times. It's hard to tell whether progress is being made and what the expected waiting time is.

We should show the total volume of data to be downloaded (bytes and number of files) and the progress so far. Seeing the URLs being fetched would also be helpful.

Rather than writing the progress indicator code, this could be achieved by just calling the wget command, or possibly by using some library functionality in Python.

[abyrd]

Although now that I've found the S3 bucket containing data for the entire US this is less critical.