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

src/urban_meal_delivery/db/utils/colors.py

@@ -0,0 +1,69 @@
+"""Utilities for drawing maps with `folium`."""
+
+import colorsys
+
+import numpy as np
+from matplotlib import colors
+
+
+def make_random_cmap(
+    n_colors: int, bright: bool = True,  # pragma: no cover
+) -> colors.LinearSegmentedColormap:
+    """Create a random `Colormap` with `n_colors` different colors.
+
+    Args:
+        n_colors: number of of different colors; size of `Colormap`
+        bright: `True` for strong colors, `False` for pastel colors
+
+    Returns:
+        colormap
+    """
+    np.random.seed(42)
+
+    if bright:
+        hsv_colors = [
+            (
+                np.random.uniform(low=0.0, high=1),
+                np.random.uniform(low=0.2, high=1),
+                np.random.uniform(low=0.9, high=1),
+            )
+            for _ in range(n_colors)
+        ]
+
+        rgb_colors = []
+        for color in hsv_colors:
+            rgb_colors.append(colorsys.hsv_to_rgb(*color))
+
+    else:
+        low = 0.0
+        high = 0.66
+
+        rgb_colors = [
+            (
+                np.random.uniform(low=low, high=high),
+                np.random.uniform(low=low, high=high),
+                np.random.uniform(low=low, high=high),
+            )
+            for _ in range(n_colors)
+        ]
+
+    return colors.LinearSegmentedColormap.from_list(
+        'random_color_map', rgb_colors, N=n_colors,
+    )
+
+
+def rgb_to_hex(*args: float) -> str:  # pragma: no cover
+    """Convert RGB colors into hexadecimal notation.
+
+    Args:
+        *args: percentages (0% - 100%) for the RGB channels
+
+    Returns:
+        hexadecimal_representation
+    """
+    red, green, blue = (
+        int(255 * args[0]),
+        int(255 * args[1]),
+        int(255 * args[2]),
+    )
+    return f'#{red:02x}{green:02x}{blue:02x}'  # noqa:WPS221