[RM-8212] [linemeas] fit a distinct wavelength offset and velocity dispersion on overlapping elements

Created on 2023-08-16 09:13:50 by Didier Vibert. % Done: 0

issue raised by @ytemmam when looking at SDSS fitted Ha vs direct-integration fluxes.

when several elements are overlapping (eg Ha and NII) a unique wavelength offset and width (velocity dispersion) is fitted for the complex, whereas each element should have its own offset and width. Of course the fit has still to be done jointly.