Allow different rotor average model for turbulence

py_wake/deficit_models/no_wake.py

py_wake/tests/test_deficit_models/test_deficit_models.py

py_wake/tests/test_rotor_avg_models.py

...ke/tests/test_turbulence_models/test_turbulence_models.py

py_wake/turbulence_models/crespo.py

py_wake/turbulence_models/gcl.py

py_wake/turbulence_models/stf.py

py_wake/turbulence_models/turbulence_model.py

py_wake/wind_farm_models/engineering_models.py