Remove elliptical aerosol clouds from transmission model

An AerosolCloud in the transmission model was either elliptical or circular. The elliptical shape has little effect on the simulation outcome. Circular shapes are much easier to handle and comprehend. Therefore, the elliptical shape was removed and the model simplified.

• In TransmissionModel, adapt update routines to new circular shapes; separate routines relating to aerosol clouds and droplets.
• In AttributesTransmissionModel and scenario files, change parameter aerosolCloudInitialArea to aerosolCloudInitialRadius.
• In AerosolCloud, remove deprecated (commented) code.
• In AttributesAerosolCloud, reduce the number of required parameters to describe the shape.
• Adapt and simplify all related classes that used the elliptical shape of aerosol clouds.