Merge branch 'feature/gitlab-ci' into 'master'

.gitlab-ci.yml

Dockerfile

barcode_example_generator.py

files/brightspace_export.png

files/paper_feed.jpg

files/scan_settings.jpg

files/scan_to_me.jpg

package.json

tests/data/black-a4-2pages.pdf

tests/data/blank-square-2pages.pdf

tests/data/overlays/a4-0.png

tests/data/overlays/a4-1.png

tests/data/overlays/square-0.png

tests/data/overlays/square-1.png

tests/test_pdf_generation.py

zesje/api/images.py

zesje/api/submissions.py

zesje/scans.py