[#10] system tests converted to pytest

Implemented python tests for keama.

Notes for reviewer:

The MR is currently set to merge into 1-initial-setup for easier review, but once #1 (closed) is merged, it will be rebased and retargeted to master.

There are many obsolete files being removed. All test data files were moved to keama/tests/data. This shows on gitlab as a file with zero differences.

Closes #10 (closed)