add flake8 linter and AutoPEP8 formatter

[krokrob]

this fixes lewagon/data-setup#23 @ssaunier please review

[ssaunier]

• What about Glovebox? cf:
  • https://github.com/lewagon/data-runner/blob/master/Dockerfile#L5
  • https://github.com/lewagon/glovebox/blob/master/app/services/data_science/output_parser.rb#L5 (breaking change)
• What about the Makefile in data-challenges? cf https://github.com/lewagon/data-challenges/blob/master/01-Python/01-Programming-Basics/01-Sum-Of-Three/Makefile#L4
• I guess we also need to add pip install flake8 to the setup https://github.com/lewagon/data-setup/blob/master/_partials/pip.md

[krokrob]

We don't use flake8 for syntax testing atm but it is a good linter for students inside their code ediitor. We will change pylint for flake8` in Q2 I think.

[krokrob]

I forgot to mention you in lewagon/data-setup#42

[ssaunier]

The risk of doing 50% of that change is that flake8 in Sublime Text will say something while the pylint through make will say another, don't you think it'll be even more confusing for students?

[krokrob]

pylint is much more "lazy" than flake8, as it considers devs know how to use code formatter like black or autoPEP8. Our students still need a linter as they are still programming learners. There won't be contradictory syntax error between the 2 frameworks.