Get more Python package data when scanning setup.cfg

In Python packages, the `setup.py` file can contain origin info for a package. We can determine what the license, copyright holder, homepage and download URLs, as the package owner/maintainer declared it. However, some Python packages (like scancode-toolkit and other nexB projects) declare all of the package info and whatnot in `setup.cfg`, then let setuptools handle everything else. It does not seem that we get license or holder information when we do a Package scan on a `setup.cfg`, we only get the declared dependencies.

It would be convenient to be able to get more Package information from `setup.cfg` when scanning Python packages.