Added a progress bar during the file download

I was curious to see how easy it would be to integrate the ProgressBar with Guzzle, so I implemented the TODO in the code.

There is a side effect of this change: I discovered that the bottleneck (at least on Windows) is not the download of the zip archive, but the extraction of the files to create the project. this is why I added another message in the output. It would be weird to see a progress bar reaching 100% and then waiting for minutes without knowing what happens (yes, the extraction/cleanup took more than 2 minutes)