Move usage of wavelength for scattering factor to the form factors themselves instead of doing one global precalculation

Move Particle::registerPosition() to IParticle and remove code duplication in IParticle derived classes

First step in deprecating ParticleComposition::addParticle with position information; this position should be set on the added particle

Use propagation of transformations during form factor creation: ParticleComposition & ParticleDistribution

Refactor: rename Transformation in IParticle member functions to Rotation; add position inside IParticle (not yet used)

Implemented GUI functional test for ParticleComposition (translation is now ok, but total particle density is still missing from ParticleLayoutItem in GUI)