Unify ZenodoScenarioDownloader and retrieve_databundles

[ktehranchi]

We already have another script developed for downloading and unzipping data from zenodo repositories. We should unify this script and that one to avoid duplicated code.

Original Script: https://github.com/PyPSA/pypsa-usa/blob/master/workflow/scripts/retrieve_databundles.py

Originally posted by @ktehranchi in #680