Missing T15 in EVOL?

Created by: scarlehoff

After merging #821 T15 is missing from EVOL: https://github.com/NNPDF/nnpdf/blob/fa36b1a1ec6968c0f57dbd03bea9f8f00048fd28/validphys2/src/validphys/pdfbases.py#L501

not sure whether this is intentional (and EVOL should really only have 7 flavours). Do we have a document defining all basis? From #794 I thought EVOL should have T15.