Merged requested to merge InterfaceToLHAPDF into master
Version of PARTONS interfaced to LHAPDF and APFEL++. The main new features are:
- Introduction of a full-fledged Collinear Distribution Module for handling forward distributions (i.e. PDFs and FFs) along with forward evolution.
- LHAPDF and APFEL++ are used as a particular realisation of the Collinear Distribution Module and its evolution, respectively.
- APFEL++ can now be used for GPD evolution (on the same footing as Vinnikov's code),
- LHAPDF is now used also for those GPD modules that require forward distributions.