(closes#3986)
Root cause was the vertex shadow strokes were too big, esp on endpoints.
For normal lines 16px stroke width centers on the line, but for vertices
it extends beyond the vertex radius, stealing clicks.
Also switched some "globals" to module variables in draw.js
* Reevaluate all featuers stroke widths for shadow, casing, stroke
* Shadow width is important to make sure all features are easily clickable
* Casing width is important to see oneway arrows
* Make sure all line styles have normal and low-zoom variants
* Show directional arrows for all waterway types
