Isochrones

Add support to Eden to generate Isochrones for various things, like distance to school / hospital:

• ​http://wiki.openstreetmap.org/wiki/Isochrone

See Example for Driving times to Ebola Treatments Centers in West Africa:

• ​http://maps.who.int/SimpleViewer_WHO/?webmap=adcafab67341461c84961d534316f1ba

(screenshot attached in case site goes down)