Merge branch 'UnitHandling' into 'develop'

GUI/Application/ApplicationSettings.cpp

GUI/Application/ApplicationSettings.h

GUI/Models/ItemWithParticles.cpp

GUI/Models/ParticleLayoutItem.cpp

GUI/Models/SelectionDescriptor.h

GUI/Models/Unit.cpp

GUI/Views/SampleDesigner/LayerOrientedSampleEditor.cpp

GUI/Views/SampleDesigner/LayerOrientedSampleEditor.h

GUI/Views/SampleDesigner/MesoCrystalForm.cpp

GUI/Views/SampleDesigner/MesoCrystalForm.h

GUI/Views/SampleDesigner/MultiLayerForm.cpp

GUI/Views/SampleDesigner/MultiLayerForm.h

GUI/Views/SampleDesigner/ParticleCoreShellForm.cpp

GUI/Views/SampleDesigner/ParticleCoreShellForm.h

GUI/Views/SampleDesigner/SampleEditorController.cpp

GUI/Views/SampleDesigner/SampleEditorController.h

GUI/Views/SampleDesigner/SelectionContainerForm.h

GUI/gui.qrc

GUI/images/unit_angstrom.svg

GUI/images/unit_nm.svg