coord_sf and silhouette size

[LewisAJones]

Currently, when using coord_sf with a map projection (e.g. Mollweide) silhouettes can seem like they are not plotted because they are so small compared to the y-axis range vs. the size of the silhouette. We should perhaps add a simple if statement that compares the y-axis range to the size of silhouette and message the user if a certain threshold is exceeded, perhaps if y-axis is more than 1000 times size.