Add basemap selection button to map

[amyleew]

with Leaflet Layer.control

[amyleew]

https://gist.github.com/tristen/1914fd00b59523aac1e0

[amyleew]

@tristen - Basemaps are showing up and swapping out but have questions:

• [x] Seems like each map is just show / hiding layers instead of replacing based on selection. Can I control loading so it's done individually?
• [x] layer.options.id holds the proper map label how do I set that to the control to replace the numbers?
• [ ] How do I add position from L.control.layers(mapLayer).addTo(map); Not sure on the syntax, I tried:

  .layers(mapLayer),
  .setPosition('topright')
}).addTo(map);

[amyleew]

added https://github.com/amyleew/osrm-frontend/commit/7e2dc3d065f8a7cba3c4289d06f1162fa1971f08