migration lines with directions

[GoogleCodeExporter]

The generated KML graphs may get cluttered. Adding arrows to the end of line 
segments may improve a little, representing lines as >>>>>>>>>>> may improve a 
lot. 

KML lines only allow a core and outer color: 
https://developers.google.com/kml/documentation/kmlreference?hl=nl#linestyle

Open Layers allows dashed and dotted lines: 
http://dev.openlayers.org/releases/OpenLayers-2.8/doc/apidocs/files/OpenLayers/F
eature/Vector-js.html#OpenLayers.Feature.Vector.OpenLayers.Feature.Vector.style

Still not what we need though dotted lines may result in more blending effects 
than just transparency.

Original issue reported on code.google.com by [email protected] on 3 Mar 2013 at 3:56