Use 'flux' and 'area' instead of 'luminosity' and 'volume'

[keflavich]

In order for SpectralCloudstering to work out of the box (i.e., on a ppv_catalog), it should use only default parameters, so 'flux' and 'area_exact' or 'area_ellipse' or 'radius' would be preferable to 'luminosity' and 'volume', since those have to be defined separately.

[dcolombo]

Yes, it might be possible. Currently it uses the volume to account for the velocity dispersion (a criteria that, by itself, does not provide good affinity matrices...). The volume matrix, however, is "dominated" by the area (_exact or _ellipse) criteria that works well by itself. The luminosity is used instead of the flux to account for the different distances of the Orion-Monoceros complex objects.