Revamp tests; Delete outdated; Make common conftest.py; Improve segmentation tests; Allow segmentation tests to run on CI

Make code and tests flexible to the use of a pre-processed Montgomery dataset to speed-up testing where possible (closes #74)

Some tests have been updated, while other which are still a work in
progress have been marked with @pytest.mark.skip(reason="Test need to be updated")

[tests] Simplifies test database unpacking by moving code to a pytest initializer; Make tests more unaware of the test database