MAINT: Linting tests run through now.

Summary

• Added style check and linting to Makefile and pipeline.

Focus

• Are the Makefile / pipeline commands correct?
• Are the fixes to the code OK? (Or else, are they covered by new issues such as #80?)

Test Environment

make style
make lint
pip install -U . && make unittest
cd integrationtests && ./test.sh # (Or believe in the pipeline instead).

Check List for the Author

• All automated tests pass
• Reference related issues #67 (closed)
• Up-to-date CHANGELOG.md (or not necessary) -> No real changes to the code.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.