Get model_name from model class on loading checkpoint

[pjbull]

To fix #220, we add a _default_model_name property to each model class. This allows us to look up the config specifications for a loaded checkpoint based on the model class (not just the name). We also use a utility function with lru_cache to make sure we don't have to load large checkpoint files more than once to get the hparams.

Bonus fixes:

• Add a make format command to run black
• Add docs fix to remove typo
• Add save_dir to the tests so that nothing gets written to local folders
• Add removing .DS_Store files to test cleaning

Closes #220

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[github-actions]

🚀 Deployed on https://deploy-preview-221--silly-keller-664934.netlify.app

[ejm714]

Code all looks good, but can you look into the failing tests?

[codecov-commenter]

Codecov Report

Merging #221 (810623d) into master (e30c2ae) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##           master    #221     +/-   ##
========================================
- Coverage    87.0%   86.8%   -0.2%     
========================================
  Files          29      29             
  Lines        1919    1903     -16     
========================================
- Hits         1670    1653     -17     
- Misses        249     250      +1     

Impacted Files	Coverage Δ
zamba/models/config.py	97.1% <100.0%> (-0.2%)	⬇️
zamba/models/efficientnet_models.py	100.0% <100.0%> (ø)
zamba/models/model_manager.py	83.9% <100.0%> (-0.2%)	⬇️
zamba/models/slowfast_models.py	88.8% <100.0%> (+0.3%)	⬆️
zamba/models/utils.py	100.0% <100.0%> (ø)
zamba/version.py	80.0% <0.0%> (-20.0%)	⬇️
zamba/data/video.py	80.8% <0.0%> (-0.7%)	⬇️
zamba/models/densepose/config.py	92.2% <0.0%> (-0.2%)	⬇️