Protzilla overhaul tests

[JanniRoebbecke]

Description

• adapts some tests to the refactoring

Changes

• changed tests of specific methods (import, data_analysis, data_integration) to accept the new input and output format
• more intense changes in run_test and step_tests to account for the new structure of thous
• minor fixes in data_preprocessing and importing methods (not tests, but the actual code)
• major reworking of remove_step function in steps.py. As far as I can tell this didn't really work before and a lot of the edge cases did not make a lot of sense

Testing

• check if all tests test the same thing as they did before
• check if all tests, that have been touched in this pull request pass now (by running the tests)

PR checklist

Development

• [x] If necessary, I have updated the documentation (README, docstrings, etc.)
• [x] If necessary, I have created / updated tests.

Mergeability

• [ ] main-branch has been merged into local branch to resolve conflicts
• [ ] The tests and linter have passed AFTER local merge
• [ ] The code has been formatted with black

Code review

• [x] I have self-reviewed my code.
• [ ] At least one other developer reviewed and approved the changes