Spherical Shell

Description
The spherical shell primitive is defined by its central point, radius and thickness. It is created with CSX = AddSphericalShell(CSX, propName, prio, center, rad, shell_width, varargin) with the following parameters:
 * CSX: The original CSX structure
 * propName: name of the assigned property
 * prio: priority of the primitive
 * center: coordinate of the center point of the sphere
 * rad: radius of the spherical shell
 * shell_width: thickness of the shell
 * the inner radius of this shell is rad-shell_width/2
 * the outer radius of this shell is rad+shell_width/2
 * varargin: a key/value list of primitives variable arguments

Example
CSX = AddMetal(CSX,'metal'); %create PEC with propName 'metal' CSX = AddSphericalShell(CSX,'metal',10,[0 0 0],50,10);
 * Create a metal sphere at (0,0,0) with radius 50 and thickness 10: