Speed up healthsite distance query by using healthsites.io API

[msradam]

Healthsites.io does have their own API, and it may be useful to make requests to it by specifying latitude and longitude and obtaining a list of healthsite points. This way the algorithm can narrow its search for closest healthsites. This could be done by creating a latitude and longitude based bounding box from the list of source points (e.g. schools), then querying the healthsites API based on that bounding box, so the only healthsites returned are the ones guaranteed to be within this bounding box.

This is advantageous for large countries with a lot of data to process, but may lead to missing data if a faster road is outside of that bounding box.