Updated all the examples' YAML files to use the new periodic flag.

examples/MultiTypes/multiTypes.yml

examples/Noh_1D/makeIC.py

examples/Noh_1D/noh.yml

examples/Noh_2D/makeIC.py

examples/Noh_2D/noh.yml

examples/Noh_3D/makeIC.py

examples/Noh_3D/noh.yml

examples/PMillennium-384/p-mill-384.yml

examples/PMillennium-768/p-mill-768.yml

examples/PerturbedBox_2D/makeIC.py

examples/PerturbedBox_2D/perturbedPlane.yml

examples/PerturbedBox_3D/makeIC.py

examples/PerturbedBox_3D/perturbedBox.yml

examples/SantaBarbara/santa_barbara.yml

examples/SedovBlast_1D/makeIC.py

examples/SedovBlast_1D/sedov.yml

examples/SedovBlast_2D/makeIC.py

examples/SedovBlast_2D/sedov.yml

examples/SedovBlast_3D/makeIC.py

examples/SedovBlast_3D/sedov.yml