Added tests for newer modules

[ipcamit]

• Fixed but in voigt stress conversion functions
• Fixed implicit fingerprinting bug in configuration transforms
• Fixed documentation and typing inaccuracies
• Added tests for ASE dataset/configuration interactions
• Added tests utils (stress functions currently)
• Added tests for configuration transformations
  • libdescriptor integrations and comparison with older modules
  • graph generations
  • Abstract ConfigurationTransform class
• Added tests for PropertyTransform

I think this covers test cases for most of the newer contributions. Let me know if I missed something. I would start working on the trainer modules now.

[mjwen]

Looks great! Just have a minor question. See above.