Better state reloading
Capture NULL labels in dependencyTree
Add general purpose directive valueWatch

Takes an object and a property. Not much - displays the property
and reflects its changes.
Use a directive for edgeLabels in dependencyTree

This brings a huge speed up in the tree. We don't have to rerender the
whole tree if we only change a label.
We can now make changes to it in place, which is much snappier.