Implement validators on CarbonFootprint

[JohnVonNeumann]

CarbonFootprint is only partially completed, the core datatype is there and the tests show that values can be provided to the relevant compulsory attributes, but there is basically no validation on the type itself, only on the subtypes that it uses in aggregate, also the docstring is not completed. Ultimately didn't have the time or patience to fuck around with the other bits right now, just wanna get the final ProductFootprint done, so that all the datatypes are in there and I can move towards compulsory conformance prior to the next connectathon deadline.