Add error checking for input config file

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Need to write some input checking and error handling for config file with helpful messages

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Tools I found that may help:

https://stackoverflow.com/questions/3262569/validating-a-yaml-document-in-python

User "Cerberus"? (because excellent docs) https://github.com/pyeve/cerberus https://docs.python-cerberus.org/en/stable/

Also, "Schema" https://github.com/keleshev/schema

Also, "Pykwalify" (schema is just another easy-to-read yaml file) https://github.com/grokzen/pykwalify

Also, "Yamale" https://github.com/23andMe/Yamale

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Add more error checking code on the loaded configuration file (example: so we do not create crazy-large xml files if someone says there are one million students). Some ideas for config file restrictions:

• Only two user type allowed (trainer and student)
  • Maybe three for flexibility
• Up to 4 trainers allowed
• up to 12 of any other type allowed
• Up to 10 device types allowed
• up to 10 devices per type