Adding setup.cfg config file (flake8 & isort) and poetry script commands

[PieterjanMontens]

• adding setup config file for flake8 & isort (and make them black-compatible)
• adding ./server.py file and poetry run scripts to allow poetry run server instead of poetry run python manage.py runserver (could be done with a dependency like poe instead of ./server.py file)

[PieterjanMontens]

At this moment environ and sentry are only installed with poetry install -E environ -E sentry, as they are considered optional. If the user doesn't install sentry or environ, the server won't run.