Potential GraphVisualizer improvements

[RobertObkircher]

• It would be nice to include the source code in the final svg.
  • In Simple-Rust I print digraph "escaped source code" { instead of digraph chapterXY { /* source code */, so it can be seen by hovering over empty space. I haven't checked if this works on touch devices though.
• findAll should return a list sorted by _nid to make the output independent of javas HashMap.Values iteration order.
• nodesByCluster mutates the node outputs. This is not a problem, but it might be nicer so sort a copy to keep the visualizer side-effect free.