Add drop shadow to state outlines

[travissouthard]

Overview

To fulfill @svandekerkhof's vision, we need to add dropshadows to the state outlines on hover (and ideally to the whole map as well)

Is your feature request related to a problem? Please describe.

We want the map to look like this:

Describe the solution you'd like

In poking around, it looks like neither drop shadow or box shadow (nor any other shadow belonging to css) are available in the PathOptions (which control styling for features), but it does include className and we can use that to set and unset the class and add a drop shadow or box shadow via css in index.css