Updates to map component

[paylakatel]

This PR:

• brings back feature counts so we can display them on the map
• changes how we render the map from leaflet to mapboxGL to improve performance
• adds a heatmap layer on zoom out
• makes sure the pop-ups display information about all the crashes if a user selects multiple points
• sort of deals with timezones by adding 5 hours to our dates - a method that may need to be made more robust in the future