Store soil, road, and weather data locally

Fetching external data from soilgrids, weather service, or osm-overpass takes a considerable amount of time. It is unnecessary for repeated processing when people play with different config parameters for the same dataset over and over again.

We should store the downloaded data or variable[coordinate] dict somewhere locally, just as it is already implemented for incoming radiation (NM) or the road network via osm-nx (see e.g. corny/exdata/openstreetmap.py:Graph.load().