Gitlab ci

Add pytest-workflow tests and enable gitlab-ci integration, including the slurm runner.

.gitlab-ci.yml

+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
+.before_script_anchor: &before_script_anchor
+  before_script:
+    - pip3 install pytest-workflow
+
+stages:
+  - sanity
+  - dry-run
+
+test-sanity:
+  <<: *before_script_anchor
+  script:
+    - pytest --tag sanity
+  image: lumc/singularity-snakemake:3.5.2-5.15.0
+  tags:
+    - docker
+  stage: sanity
+
+test-dry-run:
+  <<: *before_script_anchor
+  script:
+    - pytest --tag dry-run
+  image: lumc/singularity-snakemake:3.5.2-5.15.0
+  tags:
+    - docker
+  stage: dry-run