Add extra grib2/cf translations : Fix bug in grib_phenom_translation.

Adds 3 new Grib2 translations, needed for local user task (ref: SCIT-240).

Also fixes existing trivial bug in grib_phenom_translation.py :
It *had* been scanning the wrong _grib_cf_map dictionary to make the output lookup table _GRIB2_CF_TABLE
  -- i.e. using CF_TO_GRIB2 instead of GRIB2_TO_CF
These two were previously the same (except with key/value swapped), but no longer because the new 'land_binary_mask' translates the same as 'land_area_fraction'  -- and hence appears in the 'output' one *only*.
It was also necessary to fix the units definition for 'grib_physical_atmosphere_albedo'.  This had previously been fixed in only one dict (and the wrong one at that !).  Now is "%" for both input + output.