Resolve "BE: Migrate devtools (the easy ones)"

Closes #60 (closed)

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• .gitlab-ci.yaml SJ/KW
• commitlint-branch RK/DT
• lint-dockerfiles RV/AF
• lint-json-files RV/AF
• lint-markdown-files RV/AF
• lint-markdown-links RK/DT
• lint-pkg-json RK/DT
• lint-shell-scripts RK/DT
• squash KW/SJ
  • .gitlab/mergerequest-templates goes with it

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git commit ...
git pull --rebase && git push