Sub-grid water ice clouds in Mars PCM

There is a simple parametrization of sub-grid water ice clouds implemented in the Mars PCM. It is by default deactivated and it has not been used in some time, so it is not sure that it currently works.

It can be activated with the flag "CLFvarying" in the callphys. And it is documented in the PhD thesis by Alizée Pottier, which can be found at: https://theses.hal.science/tel-01528574

It includes an independent calculation of water saturation in the file "tcondwater", that is weird because the rest of the model uses the saturation computed in watersat_mod, and that might require some analysis and review.