Bugs in data implementations - 'easy' fixes

Created by: wilsonmr

Some datasets were found to have some bugs which need fixing raised in NNPDF/nnpdf#903 but opening a seperate issue here for the ones which are 'easy' to fix

DATA_LHCBZEE2FB

Check the index of systematics match for add and mult

DATA_D0R2CON

This needs deleting in NNPDF/nnpdf

DATA_LHCBW36PB

Check the central value used to calc mult/add error

DATA_CDFZRAP

Check sign of experiment covmat