Add more aerosol info, aerosol calc list, and constants section.

Also add subsection for difference colorbar options and flag for non_linear scale plotting/color scale

This moves away from the nco way of deriving variables and moves it to xarray. This is mostly so that any derived variable that has more than two constituents can be processed. The nco way only worked for two constituents.

Also add check for any aerosol variables that will require rho (density of dry air) and create PMID and T time series files (if not already requested). Additionally, add section in derived variables to calculate aerosol values.

Clean up derived variable function to grab coordinates and dimensions for new variable netcdf file. Also, remove constituents from derived variable file since they will have their own.