AKARI scipack explicitly separate from Spitzer scipack?

[karllark]

I've spend sometime thinking about PR #83. It is really the AKARI+Spitzer scipack. This PR is fine as it is and should be merged once discussion is resolved.

For the future, would it be better to have the AKARI scipack only include features in the AKARI wavelength range? This would enable people wanting to fit AKARI only. This would require modifying the input for running pahfit to allow for multiple scipacks to be input.

Or should be have scipacks that include all possible features at all wavelengths and trim the features to be fit based on the observed data that is input? Currently we are really not splitting the sci and inst packs - they are really combined into one. If we went this route, our scipacks need to become object/science area specific (e.g., exgal) and then have explicit instpacks for different instruments. The scipacks would need to indicate which features are resolved (PAH features) and unresolved (gas lines) and the instpacks would provide the instrumental resolution for the unresolved lines and wavelength range for the instrument.