Add a license_utils module to dcicutils (C4-1048)

[netsettler]

In service of Programmatic checking of license compatibility (C4-1048):

This adds a license_utils module to dcicutils that in particular will allow us to do tests like this in other repos:

from dcicutils.license_utils import C4InfrastructureLicenseChecker

def test_license_compatibility():
    C4InfrastructureLicenseChecker.validate()

NOTE WELL: This relies on the pip-licenses being a dev dependency of any repo wanting to do that. I don't know how to export a dev dependency, and am not sure you can, so there is a little dance at the top of the license_utils.py file that checks to see if the repo managed to be there at all, since we don't require it in the regular dependencies. The error message explains what needs to be done.

We now have a spreadsheet tracking the utility of this because it got complex.

I have extended this to have a contribution_utils as well, tracking contributors so that we can review them to make sure we know who's been involved.

[coveralls]

Pull Request Test Coverage Report for Build 5736313253

• 665 of 665 (100.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.5%) to 77.484%

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Totals
Change from base Build 5590491337:	1.5%
Covered Lines:	8118
Relevant Lines:	10477

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💛 - Coveralls

[willronchetti]

Might be smart to import/test in another repo before merging but generally looks great and super useful for sanity checking this info

[willronchetti]

For our purposes it may be useful to be able to read this from file, so we can write top level files with this information or even a directory that can have sane defaults in utils and be overridden in other repos

[netsettler]

As a matter of design, I did not want individual repos to decide to override it. We can have several named policies. But the policies need to be approved organizationally, not at the level of coding lines. I will likely add one for pipelines.

I have tried this in a number of repos (see the list on the first page). Some problems turned up that were since fixed. Others are ongoing issues for which I may create a way to mark the license as a known problem. We can talk more about this interactively perhaps sometime.

[willronchetti]

Better to use a function scope fixture for the registry no?

[netsettler]

Me? Ha. I never use fixtures except when in a tool that already does, to not fight the style. I hate their scoping rules. Usually I'd reach for a context manager instead because I think their scoping rules are clearer. Or I'd use a class with methods that have natural static scope. I've rewritten this as a context manager in changes to be uploaded soon.