Add Regression Tests for File Versions

[electronsandstuff]

This PR adds legacy files saved to the tests directory and pytest tests which load them and confirm they still work.

• New script generate_file_version_data.py which will make a saved legacy file with synthetic data along with json representation of same data
• Add experiment_to_manifest to test utils which converts an experiment to json serializable form with summary data
• Add pytest test that reloads save file and compares to json dump
• Add pytest test that will complain if file version is updated without saving new file