Add pre-commit hooks to cleanup code

[AlexVCaron]

It would be nice to prevent contributors to commit code that doesn't abide to Scil standard. To do so, we have to configure pep8 (or flake8 or any other linter(s)) and make it so that the pre-commit hooks are installed by developpers. There is probably a way to setup the repo on cloning, but I haven't investiguated.

Here is the pre-commit hooks homepage, with all available configurations from the community. There is a lot of nice features we could use there.