Validate json file when loading configuration

[ahojukka5]

It's nice to have NaN checks:

NaNs detected on process 1 at /home/juajukka/dev/openpfc/apps/tungsten.cpp:165. Aborting MPI application.

However, it would be much nicer to validate json inputs so that all necessary things are certainly defined.

1. If something non-critical is missing, give warning and use some meaninful default
2. If something critical is missing, stop the program and describe what needs to be added

https://github.com/pboettch/json-schema-validator

[ahojukka5]

Actually there is some poor man's validation in (https://github.com/VTT-ProperTune/OpenPFC/blob/master/apps/aluminumNew/Aluminum.hpp#L308), but maybe better to implement it in a proper way.