Created function thermosoil_levels : returns depth of nodes for the thermal layers in meters.
Write correct soil depth level axis (dim solth) in history IOIPSL files and xios files insted of 1,2,3,..7.
Added solth_lev as new input variable in xios_orchidee_init : the function thermosoil_level can not be called from inside xios_orchidee module because of conflicts in dependecies.