Don't use source location to shift EPSG reference system and take source coords from dataset if available

Rename Sentinel-7 to CO2M
Add option for adding background field to Level-2 data
New attribute for scaling of anthropogenic emissions
Use different random seed for different trace gases (avoids same random
pattern for CO2 and NO2 observations in same orbit)

Add function for preparing emission time series, fitting annual emissions and comparing with true values

Add function for checking for realistic gradient in plume coords; use shortest arc length instead of shortest distance from curve for computing across-plume coords

Update plot function; new parameters for providing varnames; new parameter to use error when fitting and fixed uncertainty computation