Allow exporting with baked-in shadow
In some situations we don't get automatically rendered shadows (e.g. when using icons in mockups) so it would be nice to be able to export with a baked-in shadow.
I'm not sure how prominently we'd want to expose this in the UI, since we really want to avoid people using the icon with the shadow as their actual app icon, but it would be nice to have in some form (perhaps only as a CLI option?).