Develop final

[rowem5]

1. Updated resnet_beast.py to properly load beast checkpoints
2. Deleted code that forced one validation set. This is important to remove in datasets that are scarce and the benefit of having extra training data exceeds the benefit of a validation set.
3. Updated tests to reflect the above changes
4. Updates tests file structure to mirror our nomenclature update in the models folder
5. Added new test files for the backbone loading files.