[evaluation] Homogenize segmentation/classification code; Use more credible constructs (DRY); Fix test units

Revamp tests; Delete outdated; Make common conftest.py; Improve segmentation tests; Allow segmentation tests to run on CI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

[test/test_cli] updated unit tests for training, prediction and evaluation cli scripts. Removed radiological signs (rs) related tests