Tmatrix for Arbitrary clusters

A tmatrix option that can take any number of particles (possibly with specified constraints) and compute the cluster hologram.

Specifically, what we need is a function that will return the scattered fields for a given list of spheres. The input to the function should be a list of sphere coordinates, indices of refraction, and radii. We don't need to implement separate functions for different kinds of scatterers (e.g. dimers, trimers) -- we just need one function that will serve as an interface to the T-Matrix routines. Later we can write python code that will make it easier to calculate scattering from "special" clusters like dimers. But for now we only need the code to operate on a list of spheres coordinates.