Updated positivity in n3fit fits

Created by: juanrojochacon

Hi @scarlehoff @scarrazza one the things we agreed to do in Varenna was to verify that the n3fit code was able to properly include the new positivity observables, namely those that were not part of NNPDF3.1 (basically because we were not able to fit them successfully)!

In principle the data files and FK tables are ready, it is just a matter of verifying that the code can deal with them (hopefully, else we are a bit stuck). The new positivity files are

DATA_POSDYC.dat
DATA_POSDYCBSB.dat
DATA_POSDYCSB.dat
DATA_POSDYUBD.dat
DATA_POSDYUD.dat
DATA_POSDYCBD.dat
DATA_POSDYCD.dat
DATA_POSDYUBDB.dat
DATA_POSDYUDB.dat
DATA_POSDYCBDB.dat DATA_POSDYCDB.dat
DATA_POSDYUBS.dat
DATA_POSDYUS.dat
DATA_POSDYCBS.dat
DATA_POSDYCS.dat
DATA_POSDYUBSB.dat
DATA_POSDYUSB.dat

Furthermore, to avoid surprises at a later stage it would be great if someone, perhaps @felixhekhorn could check the calculation of the positivity FK tables, using some standalone code. We have found issues with the positivity observables a lot of times in the past so better safe than sorry.

I would really like to verify that n3fit can deal with the updated positivity constraints before it is too late. I am more than happy to assist with this!