Merge arome rain_ice with:
- Ryad's versio: optimisation, KPROMA blocs
- Meso-NH version: subgrid precipiation
Arome aux:
- mode_ll to provide get_indice_ll
- mode_budget

Known issues:
- Bug around KPROMA blocs: results are different when used
- precipitation fraction cannot be used as long as condensation is not merged
- mode_ice4_sedimentation_momentum is still not plugged

gradient* files are merged and moved in externals
shuman moved in externals
modification of arguments order for shuman and gradients

- mv *.f90 *.F90
- bug corrections in bl89 and compute_bl89_ml
- code modification to take into account the new interface of
bl89 and compute_bl89_ml
- introduction of the REPRO48 compilation key