Update default carbon intensity values to be country specific

[lfwa]

This PR includes the following changes:

1. Updated default/fallback value for when live carbon intensity cannot be fetched. We now use the latest average for the specific country detected using data from https://ourworldindata.org/grapher/carbon-intensity-electricity.
2. If above fails, default to world wide average carbon intensity for 2019 of 475 gCO2eq/kWh instead.
3. Include script to generate small csv file used in 1. from larger csv file from https://ourworldindata.org/grapher/carbon-intensity-electricity.
4. Update .gitignore with GitHub's Python template (+ VS code and macOS specifics)

The update requires thepkg_resources import, which should be available through setuptools but it might not be available in Python <3.7. Might want to consider dropping support for Python 3.6 (see also #48).

Testing is recommended.