POI: use icons rather than color labels

This would need to change both the legend and what we render on the map.

If it makes things easier for us, I imagine we could find some usable icons in our existing icon font. Though I imagine eventually we'll find one that's not supported by our font.

The issue mentions changing the legend and map rendering from color labels to icons. Look for map rendering code and legend components. Check if there's an existing icon font in the project. Start by finding where POI (Point of Interest) labels are currently defined and rendered, then see how to integrate icons. Testing will involve verifying icons appear correctly on the map and in the legend.

Written by the indexing model from the issue text.