Draft:updated dependencies in install-xfitter

I am opening this merge to update to more recent version the dependencies installed by install-xfitter. I have tested compilation and standard example work on NAF.

To compile the most recent APFELXX I had to add a setup of a more recent cmake version than what available on centos7. I also removed from the script the pieces referring to SLC5, I guess nobody would ever use it anymore, and the script wouldn't work as now cern afs is decommissioned. The only dependency I couldn't update is LHAPDF, as the latest 6.4.0 version seem not to work with Hathor.