Update Flake8 rules

[RodneyCodess]

Note: This PR is based on #26. The diff between them can be viewed here.

Description

This PR makes changes to .github/workflows/python-package.yml and docs/developing.md for style errors.

• The PR adds in additional Flake8 packages to detect and fix more style errors, more specifically quotes and comma errors.

• The PR updates .github/workflows/python-package.yml to add in the additional Flake8 packages to check for the errors we couldn't see before.

• The PR adds additional steps to download the new packages, Flake8-commas and Flake8-quotes for detecting the comma and quote errors.

Tests performed

Once we installed the new packages Flake8-commas and Flake8-quotes we kept running flake8 tests until we fixed all style errors detected by the packages.

Types of changes

• Refactoring / documentation update (non-breaking change which does not change functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• CHANGELOG.md has been updated
• The milestone is set correctly on the pull request
• The appropriate labels have been added to the pull request
• Running the automated tests (see docs/developing.md) produces no errors
• Updates have been made to the xdmod-notebooks repository as necessary, and the notebooks all run successfully