Add leaflet maps to pkgdown site

[jmhatch]

It might be nice to have a component (with a drop-down menu) on the navbar of the pkgdown site that shows a leaflet map for each of the housed spatial data sets. That way a user can get a very quick glimpse of the underlying data as a leaflet map. If the users wants to play around with the data or wants a more detailed view, then they can run @kimberly-bastille's R shiny app. Or does this sound kind of duplicative?

[andybeet]

So would the drop down would be a list of all data sets, each one pointing to an rmd with a leaflet map?

[jmhatch]

@andybeet Exactly. There would be a drop-down menu with a list of all the data sets, and each menu item would link to an rmd with a leaflet map showing that data set. But nothing fancy, it'd be pretty basic.