Switch to xarray where appropriate

docs/notebooks/EngineeringWindFarmModels.ipynb

docs/notebooks/Introduction.ipynb

docs/notebooks/Quickstart.ipynb

docs/notebooks/RunWindFarmSimulation.ipynb

docs/notebooks/Site.ipynb

docs/notebooks/WindTurbines.ipynb

py_wake/aep_calculator.py

py_wake/deficit_models/fuga.py

py_wake/deficit_models/gaussian.py

py_wake/deficit_models/gcl.py

py_wake/deficit_models/noj.py

py_wake/examples/compare_wake_models.py

py_wake/examples/hornsrev1_example.py

py_wake/flow_map.py

py_wake/rotor_avg_models/rotor_avg_model.py

py_wake/site/_site.py

py_wake/site/shear.py

py_wake/site/wasp_grid_site.py

py_wake/tests/check_speed.py

py_wake/tests/test_deficit_models/test_noj.py