Optimize vertex rendering

* Cache icon
* Append rather than insert
* Do fewer things on update
* Don't create a fill unless needed
* Don't apply tag and member classes (never used)
* Drop down to raw setAttribute (d3 is slow :trollface:)

css/map.css

@@ -73,7 +73,7 @@ g.point.active, g.point.active * {
 /* vertices and midpoints */
 
 g.vertex .fill {
-    fill: none;
+    fill: #000;
 }
 
 g.vertex .stroke {
@@ -86,10 +86,6 @@ g.vertex.shared .stroke {
     fill: #aaa;
 }
 
-g.vertex.tagged .fill {
-    fill: #000;
-}
-
 g.midpoint .fill {
     fill: #ddd;
     stroke: black;