separate theorydb into nnpdf_data

doc/sphinx/make_theory_csv.py

doc/sphinx/source/data/data-config.rst

nnpdf_data/nnpdf_data/theorydbutils.py

nnpdf_data/nnpdf_data/utils.py

validphys2/src/validphys/commondataparser.py

validphys2/src/validphys/core.py

validphys2/src/validphys/plotoptions/core.py

validphys2/src/validphys/scripts/vp_checktheory.py

validphys2/src/validphys/tests/test_theorydbutils.py

validphys2/src/validphys/theoryinfo.py

validphys2/src/validphys/utils.py