AeroProblem should throw an error when an unsupported kwarg is passed into the initialization

Description

Andrew from AERO740 found that when xref, not xRef is passed into AeroProblem(), the initialization is just fine even though nothing is happening.
I think baseclasses should return an error.

1. This could be modifying the AeroProblem python code to check a list of all supported keyword arguments. Return an error if the supplied arg does not exist in the supported keyword arguments.
2. Another method could be changing the function signature of the __init__() to list out all the kwargs.

I am open to hearing other approaches too.

Steps to reproduce issue

Something like
ap = AeroProblem(args=args, unsupportedArg=randomValue)
or rather
ap = AeroProblem(xref=0.5) does not return an error that you're not setting xRef as intended

Current behavior

…
Does not throw an error for unsupported keyword arguments in AeroProblem instantiation.

Expected behavior

…
Throw an error for unsupported keyword argument

Code versions

• Operating System:
• Python:
• OpenMPI:
• CGNS:
• PETSc:
• Compiler:
• This repository:

Locate the AeroProblem Python class and inspect its init entry point, then run the reported xref and unsupportedArg examples. Compare the accepted initialization arguments with the documented names and add coverage for rejecting unsupported keywords. Done means a misspelled or unknown keyword raises an error while supported initialization still works.