Enforce flake8 conformity
On https://www.tryton.org/develop#coding-guidelines we talk about conformance to pep8 but the current code is not 100% conform. So it is difficult to enforce it for new contribution because reviewbot generate some false positive error. Also new contributor may be astonished and perturbed by error messages not linked to their change.
So I propose to make code conform once for all and then block patch without reviewbot OK.
To make the code conform, we need to skip also W503 because bit operators are used by python-sql as boolean operator. So it is more logical (and it is the style that is most commonly used today).
Also as flake8 check configuration from the repository, we should add a .flake8 configuration.
Finally there are few cases that can not be solved like long line in tests/__init__.py. For those, we should add a noqa comment.