Reference Dataset for Testing and Training on Anatomical Variations

[yw7]

We should consider using the dataset referenced in the following paper for testing and training to better account for anatomical variations in CT images:

https://doi.org/10.1038/s41597-021-01060-0

OSF Reporsitories:
VerSe'19: https://osf.io/nqjyw/
VerSe'20: https://osf.io/t98fz/

Some examples using this dataset on #75:

11 Thoracic Vertebrae ✅	4 Lumbar Vertebrae✅	6 Lumbar Vertebrae❌	6 Lumbar Vertebrae✅

Note: The current main branch is also support 4 and 6 lumbar vertebrae when full field of view is provided:

4 Lumbar Vertebrae✅	6 Lumbar Vertebrae✅