Move to an included CI configuration file

This makes it easier to debug CI and does not pollute the repo with
useless commits.

.gitlab-ci.yml

@@ -1,65 +1,3 @@
-stages:
+include:
-  - test
+    - project: 'community/tutor-ci'
-  - build
+      file: 'tutor-gitlab-ci.yml'
-  - deploy:images
-  - deploy:pypi
-  - deploy:docs
-
-test:
-  script:
-    - make bootstrap-dev
-    - make test
-
-build:images:
-  script:
-    - make ci-bootstrap-images
-    - tutor images build all
-  stage: build
-
-build:docs:
-  script:
-    - pip install -r requirements/docs.txt
-    - make docs
-  artifacts:
-    paths:
-      - docs/_build/html
-  stage: build
-
-build:pypi:
-  script:
-    - make bootstrap-dev
-    - make build-pythonpackage
-  artifacts:
-    paths:
-      - dist/
-  stage: build
-
-deploy:images:
-  script:
-    - make ci-bootstrap-images
-    - docker login -u "$DOCKER_USERNAME" -p "$DOCKER_PASSWORD"
-    - tutor images push all
-  only:
-    - tags
-  stage: deploy:images
-
-deploy:pypi:
-  script:
-    - make push-pythonpackage
-  dependencies:
-    - build:pypi
-  only:
-    - tags
-  stage: deploy:pypi
-
-deploy:docs:
-  dependencies:
-    - build:docs
-  script:
-    - rm -rf /var/www/docs.tutor.overhang.io
-    - mv docs/_build/html/ /var/www/docs.tutor.overhang.io
-  only:
-    - tags
-  tags:
-    - private
-  stage: deploy:docs