Merge branch 'feat-ci-linting' into 'master'

Linting with CI pipeline

See merge request rc/self-reg-form!1

.gitlab-ci.yml

+image: "python:3.7"
+
+before_script:
+  - python --version
+  - pip install pylint
+
+stages:
+  - lint
+
+linting:
+  tags:
+    - lint
+  stage: lint
+  script:
+    - pylint --ignore=tests.py --max-line-length=120 *.py app