Combined commit of datafiles (update_datafiles) and enabling make dist from Sasha (fix_issue_XFITTER-45)
Combined commit containing
- clean up of datafiles, i.e. leaving only HERA1+2 data files used in combination by default (branch update_datafiles)
- fixing and enabling make dist from Sasha (fix_issue_XFITTER-45) which, after TAG is created from master, will produce tar.gz file with a new release (no further modifications like version number or clean up is needed)