changed MetaModel to PCE in examples

examples/OHagan-function/example_OHagan.py

...les/analytical-function/example_analytical_function.ipynb

...les/analytical-function/example_analytical_function_gp.py

...nction_sequentialdesign/example_analytical_function.ipynb

...-function_sequentialdesign/example_analytical_function.py

examples/beam/example_beam.py

examples/borehole/example_borehole.py

examples/convergence/example_trainingconvergence.py

examples/ishigami/example_ishigami.py

.../only-model/example_analytical_function_NoSigmaMetaMod.py

examples/only-model/example_analytical_function_noMetaMod.py

examples/pollution/example_pollution.py

examples/pollution/example_valid_pollution.py

..._component_analysis/example_principalcomponentanalysis.py

examples/sinusoidal-function/test.ipynb

...es/umbridge_tsunamitutorial/example_umbridge_testmodel.py

...ridge_tsunamitutorial/example_umbridge_tsunamitutorial.py

examples/umbridge_tsunamitutorial/testmodel.pk1

src/bayesvalidrox/post_processing/post_processing.py