Support serving local scripts first, use CDN as fallback

I created Use Geofield and Leaflet modules for maps, to respect user privacy #81, suggesting to use Geofield module with the Leaflet module in the Starshot project.

Sorry for the noise, I was mistaken: OpenStreetMap uses Fastly to serve its tiles, OSM uses CDN for instant updates | Fastly.

I mistakenly thought the polyfill.min.js file was the cause, but it is only loaded if a user actively enables lazy load (cool feature by the way!) and also from polyfill-fastly.io -- so for everyday use polyfill.min.js is not loaded.

Thanks @ressa for all this 🙏

Yea, that was a bit of a wild goose chase :) But as a positive side effect, I learned about the cool Lazy load feature. Thanks for making it @itamair, it works perfectly, only loading the tiles, as the maps scroll into view.