=== NOTES for developers ===
An attempt to keep a running log of what has been done. Latest first
=== 2014-06-23 ===
Emphasized PixelNucleus and NucleusMode over JunctionNode. May be able to get rid of the latter.
PROBLEM? How to specific root node? Can we assume tree is either:
- circular with root at centre
- orthogonal with node at left/right/top/bottom
- unrooted (in which case take any