Update to version v2.1

Updates the transmission model, that is the transmission and dose response are treated as two different submodels.

• Refactor software architecture: The previous concept of the TransmissionModel is now divided into exposure (AbstractExposureModel) and dose response (AbstractDoseResponseModel).
• Introduce new ExposureModelHealthStatus and DoseResponseModelInfectionStatus for pedestrians
• Remove InfectionStatus that was inspired by compartmental susceptible-exposed-infectious-recovered models
• Adapt GUI: add agent coloring related to the health status and opacity of aerosol clouds
• Replace deprecated data writers
• Migrate the scenario files