Addition of gas information in spectral data cubes.

[kateharborne]

Incorporating the addition of emission lines in the spectra using ProSpect features.

Additions needed include:

• Working with both the gas and stellar information when in mode="spectral" - relevant gas particle/cell properties such as elemental abundances necessary to be included for each spaxel.
• Assumed dust attenuation laws? Necessary to make clear that these are models and not produced in the underlying simulation. Likely to work with the models from ProSpect - i.e. Charlot and Fall model for birth cloud and screen dust attenuation and re-emission from MIR to FIR flux via the incorporation of the most recent Dale dust templates that model the heating of dust by a radiation field and AGN.