(re: #3003 / #4602)
For now, drawHover is commented out. Still not sure what I will do with it.
This means that things flicker a bit when dragging, also connecting nodes
(and closing lines) does not currently work.
There was lot going on preventing the vertices from rendering while dragging.
1. `modeDragNode` needed a proper `selectedIDs()` function that works like other
modes.. Many other places in iD (including the vertex renderer) call `context.selectedIDs()`..
This means that `modeDragNode` needs a new function `restoreSelectedIDs()` to do what
`selectedIDs()` was previously doing (a place to store selectedIDs so that we
can reselect those entities after the user is done dragging a node in select mode)
2. Just so many things in svg/vertices.js
- siblingAndChildVertices was missing some things for points that we render
as vertices (points in wireframe, points with directions)
- the sibling vertices weren't being included in the `filter` function, so
would disappear when doing differenced/extent redraws
- probably some other things
(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
