Extract bounding boxes for FloraWeb species details

While the bounding boxes provided with the GeoJSON all refer to the bounds of Germany, manually computing the bounding boxes based on the geometry itself seems to work. However, for widely distributed species like maple trees, these files are quite large (multiple megabytes) and take quite a bit of time to transfer. Hence this MR also switches the FloraWeb harvester to use isolated responses to significantly reduce the server load as a mitigation measure for the more costly individual requests.