Best node selection is obscure and not working properly

[heijul]

Currently, the best node is simply the one that was selected for most routes.
This seems to work most of the time, but probably selects non-optimal nodes sometimes.
The best route selection should also work on multiple, detached routes.

• Check if the way we currently select the best nodes works properly
• If it does:
  • Document, how and why
  • Recalculate the node scores for the full route.
• Otherwise:
  • Find a better way
  • Document, how/why this works better/at all.