Special grids handling
Grids like DEM, LUS, ski runs, glaciers, etc should be handled in a unified way but also with more flexibility than forcings. Therefore, we could have the following in the ini files:
FORCING2D_GRIDS = NETCDF
SPECIAL2D_GRIDS = ARC SPECIAL2D_GRIDS_FIELDS = LUS SKIRUNS
In this case, all forcings would be read using the NetCDF plugin as well as the DEM and other special grids but the LUS and SKIRUNS grids would be read using the ARC plugin (with fixed naming scheme).
From the caller, everything would be accessed by calling getMeteoData() with the MeteoGrids parameter of choice.