Add "Days Open" Metrics; Validate Issue Labels; CirPy.org AWS Transition; Misc Maintenance

[sommersoft]

This PR got a little out of hand, as multiple things got rolled into it.

Add "Days Open" Metrics

• Calculates the number of days that an issue or PR has been open.
• Applies to circuitpython_libraries and update_cp_org_libraries.
• Appends the number of days open to the issue/PR on reports

Validate Issue Lables

• Adds a new validator to check the available issue labels on each library.
• Standard labels are: bug, documentation, enhancement, good first issue

circuitpython.org/libraries Transition to AWS

• Removes the check that ensured update_cp_org_libraries was only run once a week, on a certain day. New system will run daily.
• Removes the function & call that created a PR to the circuipython-org repo with updates to libraries.json. New system will rely on using the -o command line argument to output a file (will be accomplished in circuitpython-org's travis.yml).

Miscellaneous Maintenance

• In common_funcs.is_new_or_updated(), a draft/unpublished release would cause an exception. This is now handled by ensuring that published_at contains valid data.
• Handle empty repos in circuitpython_library_validators.validate_contents() in a way that allows them to be added to both the BUNDLE_IGNORE_LIST so subsequent validators aren't run, and is also returned as an in-work-repo.

[kattni]

Thanks for all the fixes!!! 🌮 🌮 🌮