Register each attribute's change event individually, rather than a huge update event.

Not tested yet...
Clean up all the for loops in per-attribute triggers
Trying to load the notebook widgets doesn't work so well right now.

Since we don't actually have that file, we'll just assume it is loaded already for now.
fix children reference access before defined
fix typo in updating children attributes that prevented the three.js object from being set correctly
Merge pull request #4 from jasongrout/registerattributes

Register each attribute's change event individually, rather than a huge update event