Add functionality for drawing folium.Maps

- this code is not unit-tested due to the complexity involving
  interactive `folium.Map`s => visual checks give high confidence

src/urban_meal_delivery/db/utils/__init__.py

@@ -1,3 +1,5 @@
 """Utilities used by the ORM models."""
 
+from urban_meal_delivery.db.utils.colors import make_random_cmap
+from urban_meal_delivery.db.utils.colors import rgb_to_hex
 from urban_meal_delivery.db.utils.locations import Location