Fix test configuration + minor API fixes

conftest.py

docs/source/tutorials/01_tutorial_getting_started.ipynb

docs/source/tutorials/02_tutorial_basic_kernels.ipynb

pytest.ini

src/pystencils/__init__.py

src/pystencils/alignedarray.py

src/pystencils/boundaries/boundaryhandling.py

src/pystencils/display_utils.py

src/pystencils/simplificationfactory.py

src/pystencils/sympyextensions/integer_functions.py

src/pystencils/utils.py