Redmine: #1858

Provide interface for disabling cache mechanism in IFresnelMap and use it from MainComputation when Monte Carlo integration is used

Move slicing of multilayer to multilayer itself and provide default implementations of top/bottomZParticles in Layer and ParticleLayout

Provide static function that slices layers of a multilayer before calculations when needed (default implementation)

Remove MultiLayer parameter of Fresnel map constructors and set the correct multilayer from MainComputation

Move region map from ParticleLayoutComputation to its base IComputationTerm and add boolean in SimulationOptions indicating if average materials should be used

Removed FullFresnelMap in favor of (smart) pointer to ILayerSpecularInfo and removed clone() from the last

Remove layer index from ILayerSpecularInfo (making the class name actually wrong, but this will be fixed later on)

Removed some code duplication in MainComputation by handling ParticleLayoutComputation and RoughMultiLayerComputation uniformly