(closes#4669)
Now instead of creating MultiLineString targets, we just create a bunch of
LineString targets. This makes the code simpler, and anyway the entity is
still there in `properties` for drawing code to decide what to do with the target.
Incidentally, this change allows iD to support an extrusion operation.
(Because each way segment has its own unique GeoJSON target now)
This makes the code a bit more consistent and lets us avoid some
hacky and probably non-performant things:
- abusing CSS classes in the draw/drag datum functions (classed `.target`)
(is this thing target? just check d.properties)
- regexing the id for `-nope$`
(is this thing a nope target? just check d.properties)
- using context.hasEntity to get a the real entity
(is this thing a real osmEntity? just check d.properties)
- fixes code like the restriction editor which uses fake ids for split ways
