Make Python 3.6-3.7 compatible via package dependencies

[gregelin]

• Fix Dependency Error When Downloading Pip requirements #1206 importlib-metadata==3.4.0 because these package versions have conflicting dependencies #1424 re: Python 3.6-3.7 compatibility
• Stay Python 3.8-3.9 compatible
• Update related dependency license tracking comments

[gregelin]

@Dav1dV Can you explain how these changes may GovReady Python libraries compatible with Python 3.6 and 3.7 while maintaining compatibility with 3.8 and 3.9? Or does working with Python 3.6 and 3.7 break 3.8 and 3.9?

[Dav1dV]

@gregelin This allows 3.6-3.7 in addition to 3.8-3.9:

The primary 3.6-3.7 blocker was the importlib-metadata==3.4 >2 v. django-bootstrap3==14.2 on Python <3.8 conflict;
however, since importlib-metadata is no longer a project dependency on Python >=3.8
(it's functionality was integrated into Python 3.8),
it can be reverted back to importlib-metadata==1.7 (latest <2) for Python 3.6-3.7 only,
resolving that 3.6-3.7 conflict.

The only other non-comment change is adding the typing-extensions==3.7.4.3 Python 3.6-3.7-only structlog dependency.

[gregelin]

@Dav1dV That explanation helps. Thanks.

[gregelin]

I tested this branch with Python 3.6.9 on macOS 10.14.4 running ./install-govready-q.sh and also pip install -r requirements.txt and am getting errors.

ERROR: Cannot install -r requirements.txt (line 182) and importlib-metadata==3.3.0 because these package versions have conflicting dependencies.

[gregelin]

Let's put this on hold and create in the future different installs for different versions of python.

[Dav1dV]

@gregelin Pls check your environment & retry
since the requirements.txt herein specifies importlib-metadata==1.7.0 not 3.3 in your error message
https://github.com/GovReady/govready-q/pull/1454/files#diff-4d7c51b1efe9043e44439a949dfd92e5827321b34082903477fd04876edb7552R356
& I successfully tested this on 3.6,7,8,9.

🤔

• Did you try in a venv?
• Did you try uninstalling importlib-metadata then pip3 install -r requirements.txt?

[gregelin]

Hmmm....I wonder if I was on the right branch...

[gregelin]

Apparently, I tested the wrong branch. The correct branch installed GovReady correctly in 3.6, 3.7, and 3.8.

I also tested to see if the adjusted packages will still work after upgrading the requirements using ./requirements_txt_updater.sh. GovReady-Q still correctly installed in python 3.6 after running upgrade.