Provide option to download all build artifacts as a zipped file

Often, build artifacts are textual log files that can benefit a great deal from compression.

At the moment, it is very inconvenient having to wait to download a 2M log file, which under compression would be less than ~100K.

My suggestion is to provide a TGZ option next to each downloadable artifact.

As a first cut, I'd be happy if all the build artifacts were rolled into one zip - as this would already produce a bundle that is far smaller than one of the log files I download at the moment.