add in-flight icing products similar to the operational IFI

[SamuelTrahanNOAA]

There is NCEP operational software called IFI that generates in-flight icing products from model GRIB2 output. UCAR has a newer version of that software, FIP2. Someone should put that inside UPP so it runs directly off of model output, in a model-independent manner. It would make an excellent replacement for IFI in the next-generation RRFS model.