I expected to be able to navigate story maps with left/right arrow keys

Awesome work on story maps lately! 🤩 

I played with the earthquakes demo, and because the navigation buttons are `<` and `>` icons, I expected to be able to use arrow keys as shortcuts. Also, because they're so far apart, navigating back and forth can be time consuming. Scrolling is a nice shortcut, but arrow keys just sound so much nicer :)

What do y'all think?