Pydantic config

[crangelsmith]

Fixes #201

• Uses pydantic for input validation
• Moves global variables from config.py to settings.py, leaving config.py for implementation of the point above.
• Added and updated tests.
• Updates in many files for the change of config.VIS_X to settings.VIS_X (X) here is a placeholder.
• Updated config.yml example file to be used in tests.

[jolaem]

This is great, thanks Camilla!

[marjanfamili]

All good

[marjanfamili]

Missing from Readme for conda installation

conda install -c conda-forge tensorboard
conda install -c conda-forge matplotlib

pip install pyyaml

[crangelsmith]

Merging as its been tested locally and Baskerville.