CircuitGraphAnalysis: validate adjacency matrices prior to trying to compute eigenvectors.

Matrices that fail:
  * zero edges
  * only self-edges (autapses)
Arbor.js: fix corner case in measurement of terminalCableLength
WebGLApplication: new function Skeleton.getPositions
Arbor.js: fix error in function clone.

The edges of the clone were not created properly.
Became evident when computing the flow centrality of an arbor
with a branching root, which needs to be rerooted, which needs
to clone the arbor.
CircuitGraphPlot: remove unnecessary check.
CircuitGraphPlot: replace I - O with (I - O) / (I + O)

So now it's a relative measurement.
Remove public field from Project

This field is not needed anymore since we're using
Guardian for permission management.
CircuitGraphPlot: option to reroot at soma prior to loading anatomical measurements.
Merge pull request #713 from fzadow/remove-public-from-project

Remove public field from Project
Remove all references to the 'ediable' property of a stack from front end

This propery is of no more use since we moved to Django and its per-object
permissions.
Remove 'editable' property of projects from back-end

This removes some permission queries when loading all projects. The
'editable' property is of no use anymore and can safely be removed.