Solid and calibration sphere (CAL) object/class.

A S4 class that provides slots to contain relevant metadata for solid sphere objects belonging to the CAL-class scatterers. This object is created using parameters specific to the outer shell. The default behavior of this object is to only reference these outer elastic shell properties with few exceptions that are model-dependent. See scatterer-class for a more detailed description on how this S4 object is organized.