Switch to a ES6 module system like Leaflet

[fox91]

It would not be bad to plan switch to ES6 module system like happened to Leaflet 1.0.

[murb]

Definitely some improvement needed here indeed, although with this change it isn't as impossible as before: https://github.com/socib/Leaflet.TimeDimension/pulls

import Leaflet from 'leaflet';
import iso8601 from 'iso8601-js-period';
window.nezasa = {iso8601: iso8601}

import 'leaflet-timedimension';

[PBrockmann]

Should be nice because the loading can be difficult.

https://observablehq.com/@pbrockmann/wms-leaflet-gca-dev https://talk.observablehq.com/t/how-to-keep-a-notebook-working/6464/20