Optimization of the SOil freezing parameterization

Soil freezing follows from the initial work of Isabelle Goutevin

Following the modification of the TRUNK since the initial implementation, issues related to the infiltration of water in the soil appeared: see summary under Infiltration_solsgeles_v3.docx​ Soil freezing infiltration problems​

Several tests have been performed to accound for sub-grid variability of soil freezing in order to limit the reduction of infiltration due to soil freezing.

Results of some tests can be found under: ​test_soil_freezing