Improve UX of overlapping icons

When icons overlap, it can be difficult to see and select specific shipments or vehicles. Options to improve the experience may include:

- Clustering icons when zoomed out so that the user can see how many entities are at a single location
- Adding pagination / scrolling / etc to info windows so that the user can browse all entities at a clicked location
- Subtly spacing the markers apart so that it's possible for a user to zoom into a specific icon