Add flake8 config files, fixed version

This is a new version of https://github.com/OCA/maintainer-quality-tools/pull/70 (reverted with https://github.com/OCA/maintainer-quality-tools/pull/80) hopefully unaffected by issue #78.

Thanks!
could we have:

    export CONFIG_DIR=$(dirname $0)/cfg

and thus avoid the small duplication?