Isochrone-Add button tool to call web service instead of the on click event.

[stefancoe]

User should click on the button/tool/control to activate the tool and then click on the map to call the web service that returns the Geojson.

[stefancoe]

Something like this should do the trick:
http://gis.stackexchange.com/questions/173354/map-onclick-limit-number-of-pins-added-to-map-leaflet-js