Rename "Air" -> "Vacuum" almost everywhere

CHANGELOG

Core/StandardSamples/ParticleInVacuumBuilder.cpp

Core/StandardSamples/ParticleInVacuumBuilder.h

Core/StandardSamples/SampleBuilderFactory.cpp

Doc/FFCatalog/fig/ff2/bornplot.py

Examples/Demos/FitCylindersPrisms_movie.py

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

Examples/cpp/CylindersAndPrisms/CylindersAndPrisms.cpp

...thon/fitting/ex01_BasicExamples/basic_fitting_tutorial.py

.../python/fitting/ex01_BasicExamples/consecutive_fitting.py

.../python/fitting/ex01_BasicExamples/minimal_fit_example.py

...s/python/fitting/ex01_BasicExamples/minimizer_settings.py

...s/python/fitting/ex02_AdvancedExamples/find_background.py

.../python/fitting/ex02_AdvancedExamples/fit_along_slices.py