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

examples/DwarfGalaxy/getIC.sh

examples/DwarfGalaxy/run.sh

examples/EAGLE_100/eagle_100.yml

examples/EAGLE_12/eagle_12.yml

examples/EAGLE_25/eagle_25.yml

examples/EAGLE_50/eagle_50.yml

examples/EAGLE_6/eagle_6.yml

examples/EAGLE_DMO_100/eagle_100.yml

examples/EAGLE_DMO_12/eagle_12.yml

examples/EAGLE_DMO_25/eagle_25.yml

examples/EAGLE_DMO_50/eagle_50.yml

examples/EvrardCollapse_3D/evrard.yml

examples/EvrardCollapse_3D/makeIC.py

examples/ExternalPointMass/externalPointMass.yml

examples/ExternalPointMass/makeIC.py

examples/Gradients/gradientsCartesian.yml

examples/Gradients/gradientsRandom.yml

examples/Gradients/makeICs.py

examples/Gravity_glass/makeIC.py

examples/Gravity_glass/uniform_DM_box.yml