Cherry-pick of "Merge branch 'update-lhapdf' into 'master'" into 1.0
Add Lhapdf to package_filters for AthDerivationExternals
See merge request !115 (merged)
@jcatmore, in the future you'll probably want to set up merge request into this branch first. Since this is the one that we actually use for the AthDerivation build.