Add theme_civilytics_map(), theme_civilytics_dark_map(), and
theme_civilytics_slide_map() for choropleths — suppress axes, ticks,
gridlines, and axis labels while preserving titles, captions, and legends.
Fix subtitle, caption, and axis text colors in theme_civilytics_dark()
which were inheriting dark ink_2/ink_3 values meant for light backgrounds,
making them hard to read on navy. Now uses navy_200/navy_300 instead.
