Revamp tests; Delete outdated; Make common conftest.py; Improve segmentation tests; Allow segmentation tests to run on CI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

[data.transforms] Properly implement ElasticDeformation so it works with images or batches; Update test case for transforms; Create new test case for image_utils; Update models to reflect changes (partially addresses #5)