Add simple distance tools

[smalers]

This is a lower priority - useful, but not currently needed.

It would be useful to enable some basic distance tools found in other GIS tools. Maybe these are Leaflet plugins. For example:

1. Distance measure. For example, sometimes we know a point on the map and want to measure a distance, such as along a road.
2. Radius measure. Similarly, sometimes we know a point and want to draw a circle around it.
3. Area calculator. Draw an irregular shape with close. This is useful when eyeballing an area.

These tools could be activated with an icon in the left side of the legend, kebab menu, or some other unassuming UI component. The tools should not be prominent because they probably won't be used that often.