Add pre-commit and move to Github Actions

[antonag32]

I think it is a good idea to add pre-commit with some goodies like black to 'modernize' this repo and adopt a definitive coding standard. We could then move the whole thing to Github Actions instead of travis, since we are just running "normal" Python tests, which do not involve setting up Odoo instances or stuff along those lines.

[pedrobaeza]

I like the idea. I think we can start applying black as a first step.