Enhance iSEDfit to be able to simultaneously fit broadband photometry and spectroscopy.

[moustakas]

Assuming the user provides photometry and spectroscopy which is spatially coincident, it would be great for iSEDfit to be able to fit all the available data simultaneously. This would require a somewhat significant extension of the data model and would have to address the multitude of issues that the spectroscopy would bring, such as velocity dispersion fitting (or more general LOSVD fitting), bad-pixel masking, simultaneous fitting (or not) of the emission lines and stellar continuum, etc.