revert accidental renaming (-> ISimulation) in Python sources

Examples/Demos/simul_demo_cyl_SSCA.py

Examples/Demos/simul_demo_cylsphere.py

Examples/Demos/simul_demo_lattice1.py

Examples/Demos/simul_demo_lattice2.py

Examples/Demos/simul_demo_movie.py

Examples/Demos/simul_demo_movie2.py

Examples/Demos/simul_demo_movie3.py

...ExtendedExamples/specular/RealLifeReflectometryFitting.py

...ation/ex03_InterferenceFunctions/Interference1DLattice.py

...mulation/ex03_InterferenceFunctions/RectangularGrating.py

...mulation/ex04_ComplexShapes/ParticlesCrossingInterface.py

...on/simulation/ex05_BeamAndDetector/RectangularDetector.py

...n/simulation/ex06_Reflectometry/PolarizedSpinAsymmetry.py

...imulation/ex06_Reflectometry/PolarizedSpinAsymmetryFit.py

Examples/python/simulation/ex07_Miscellaneous/FindPeaks.py

...s/python/simulation/ex07_Miscellaneous/MagneticSpheres.py

Tests/Functional/Python/PyCore/sliced_composition.py

Tests/Functional/Python/PyCore/sliced_spheres.py

Wrap/python/plot_utils.py