config class

[chrisdicaprio]

we need a configuration class to handle the user inputs

check:

• any files exist
• exclusive entries are not combined
• essential entries are present
• types are correct
• anything that is enumed or has restricted values meets the criteria

Required:

• vs30 OR vs30 in the site file
• SRM and GMCM lts or model version
• IMTs
• aggs (restrict to "mean", "std", "cov" or a string that can be cast to float)
• compatability key (check that it exists)
• locations (files or strings or common identifiers) get_locations() will catch this