rename calculator to simulation in apps

apps/cpu/ConvectionOfVortex/cov.cpp

apps/cpu/CouetteFlow/cflow.cpp

apps/cpu/FlowAroundCylinder/cylinder.cpp

apps/cpu/HerschelBulkleyModel/hbflow.cpp

apps/cpu/HerschelBulkleySphere/hbsphere.cpp

apps/cpu/JetBreakup/JetBreakup.cpp

apps/cpu/LaminarTubeFlow/ltf.cpp

apps/cpu/Multiphase/Multiphase.cpp

apps/cpu/MultiphaseDropletTest/droplet.cpp

apps/cpu/PoiseuilleFlow/pf1.cpp

apps/cpu/RisingBubble2D/RisingBubble2D.cpp

apps/cpu/ViskomatXL/viskomat.cpp

apps/cpu/rheometer/rheometer.cpp

apps/cpu/sphere/sphere.cpp