atm input generic_ps

Notice in the branch IOPerturbation-fram-compile, atmosphere-type: generic has changed to generic_ps. 
Thus, the folder name in NEXTSIM_DATA_DIR/GENRIC_ATM and linked origin files in /cluster/projects/nn2993k/sim/data/ECMWF_forecast_arctic_stereographic/generic_atm_20191111.nc also need to be changed consistently.