Exchange progressbar with progress (#211)

This PR addresses issue #211

I thought, I'd kick this off with a first implementation of using progress. The change was easy enough and it is easy to handle.

It still needs a test for a website with no content-header and I would need a site with a larger downloadable file without a content-header to see how the spinner works.

I know it still needs work, but I would appreciate some input, if we should go ahead with it.

Cheers 
With the needed fixes as mentioned below, I think it will be ok for now.