Need pre-commit hooks

[jdvala]

I see in a lot of PR there are flake8 and isort errors. These could be easily avoided if there pre-commit hooks are used. Also we can use black as code formatter and switch to github actions.

[jdvala]

@kvesteri I have made 2 PRs, one regarding use of Github actions and one regarding using pre-commit hooks. For github actions you have to unable github actions, secondly, for using pre-commit hooks, we might have to drop python3.4 support. However, we can continue to test python3.4 but it will be a little bit difficult to setup. I will keep looking into how to enable support for python3.4, but currently I don't see anything other option.