wip: move formatters to a module

[yohanboniface]

This mainly allows to dynamically load the third party libraries needed for converting from/to geojson, so only the needed ones will be loaded.

In the same process, those libs have changed:

• tokml => switch to placemarkio fork, more up to date and available as ESM
• togpx => switch to geojson-to-gpx, more up to date and available as ESM (note: this lib does not export polygons, because they do not make sense in GPX world, while the previous was converting them as lines before)