Generic Scattering Calculator Enhancements: integrate into fitting

[butler]

Lilo Pozo of the University of Washington suggests that she very much likes the concept of the Generic Scattering Calculator and thing it could be an extremel powerful too for SAS analyis if a few features were added. These are being broken into 3 tickets.

Once the calculted curve is a theroy curve, we should add instrumental smearing just as we do with any theory curve. Also we need to identify how the SLD is being computed and add the flexibility of using either neutron or X-ray SLDs. Finally we could allow for fitting of background and solvent SLD (i.e. contrast). This latter may require reworking the calculator itself.