Add pre-commit hooks

Automatically run:
- black
- flake8

See https://pre-commit.com

.flake8

+[flake8]
+# E501: let black handle line length
+# W503 is incompatible with PEP 8
+ignore = E501,W503

.gitlab-ci.yml

 image: docker:latest
+include:
+  - "https://gitlab.esss.lu.se/ics-infrastructure/gitlab-ci-yml/raw/master/PreCommit.gitlab-ci.yml"
 
 variables:
   NGINX_IMAGE: "$CI_REGISTRY_IMAGE/nginx"
   PYTHON_SERVER_IMAGE: "$CI_REGISTRY_IMAGE/python-server"
 
 stages:
+  - check
   - build
+  - test
   - release
   - deploy
 

.pre-commit-config.yaml

+repos:
+  - repo: https://github.com/ambv/black
+    rev: 19.10b0
+    hooks:
+      - id: black
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.4.0
+    hooks:
+      - id: flake8

README.md

@@ -8,6 +8,13 @@ This repository contains the structure to create the public opi screens running
 If you want to contribute to the screens the sequence is the following:
 
 - Install Docker on your computer and clone the git archive
+- Install pre-commit: https://pre-commit.com
+- Install the git hook scripts (only required the first time you clone the repo):
+
+  ```
+  pre-commit install
+  ```
+
 - Build the docker images with
 ```
 docker-compose build