Separate the theorydb utilities into the data package

Created by: scarlehoff

This is innocuous since the theorydb utils just define which entries the theory accepts.

This will make it easier for other programs (e.g., pineko) to use theories from here. The global definition of the theory can be done in the _TheoryCard dataclass. At the moment only the keys for NNPDF are there and they are all mandatory (even if it is not true).