Add a reactive layer to map. — addReactiveFeatures
This function adds a layer to a map that is dependent on another layer.
The reactive layer will be shown/hidden when holding the Ctrl-button on your
keyboard and performing the action defined by on. on can be
either "click" (default) or "mouseover".
Note: srcLayer needs to be added to the map using addGeoJSON
because we need to be able to link the two layers by a common attribute
defined by argument by. Linking will be done via group name
of srcLayer.