SVG Overlay: switch from Raphael to D3 (WIP)
SVG Overlay: remove mouse event catcher circles (WIP)

Instead creating larger, separate, transparent SVG circles for every
node to catch mouse events, use a large transparent stroke on node
circles to acheive the same effect with half the number of SVG elements
and operations.
SVG Overlay: replace arrow lines with markers (WIP)

Instead of having a separate line and arrow for connector edges, use a
normal line with a single defined SVG marker. Halves the number of SVG
elements required for these edges and greatly simplifies updates,
improving performance.
SVG Overlay: finish migration to D3

Now that some SVG elements have been removed or combined, finish
migrating from Raphael to D3 by fixing remaining errors and adding mouse
interactions.
SVG Overlay: outline node on hover (WIP)
SVG Overlay: place confidence labels consistently

Confidence labels for connectors were being placed below the
corresponding edge, instead of above, due to transposed self/parent
locations (or rather their analog for connectors).
scaling wip