improve and customize line-mouse-marker:

- negative zIndexOffset to have line marker under waypoint markers
- turn line marker off when over waypoint marker
- consider border width in iconAnchor (fix offset from line)
- same border color and width as line (instead of black)

css/leaflet-routing.css

@@ -1,5 +1,5 @@
 div.line-mouse-marker {
   background-color: #ffffff;
-  border: 2px solid black;
-  border-radius: 10px;
+  border: 4px solid rgba(0, 51, 255, 0.6);
+  border-radius: 8px;
 }