nnfit export and dglap improvements

Created by: scarrazza

This PR supersedes #193 and #220, closes #230 (closed).

Major changes:

• porting changes from #193 to reduce potential leaks.
• porting ExportGrid from #220.
• modified nnfit and fitpdfset accordingly to ExportGrid mechanism.
• implemented the EvolveGrid class which takes ExportGrid as input.
• all replicas can create an info file if not available.
• general cleanups (compiler warnings, closes #6 (closed) for our own code)

Fits are stored through ExportGrid and evolution is performed on top of this grid with EvolveGrid. Some simplifications and changes have been performed in comparison to master, e.g. fixed x-grid, different interpolation order for DGLAP, same x-grid for LHAPDF and APFEL, always printing all flavours.

TODOs:

• update revolve and revolvenet in evolvelha and evolvefit (after @nhartland and @Zaharid first approval)
• tests