Feature request: ignore unknown variables in config.json

[JackMostow]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is:
Unknown variables in config.json cause an error (true?).

Describe the solution you'd like
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Ignore them. Perhaps log the ignored variable and value.

Describe alternatives you've considered
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Approach to be followed (optional)
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Just add a catch-all case to the config.json parser.
Also, make sure configuration classes are accessible throughout RoboTutor.

Additional context
Configuration classes are located in: https://github.com/RoboTutorLLC/RoboTutor_2020/tree/development/app/src/main/java/cmu/xprize/robotutor/startup/configuration
While NSP questions are located in:
https://github.com/RoboTutorLLC/RoboTutor_2020/tree/development/comp_questions/src/main/java/cmu/xprize/comp_questions

What is currently in the NSP questions is the config.json is read again with only the necessary NSP-related items since the Configuration classes cannot be accessed in comp_questions