Synapse clustering: fix error in corner case of segregation index.
utils.js: new function parseArbor, to parse compact-skeleton into an Arbor,
the positions of its nodes, and count the inputs and outputs when present.
SkeletonMeasurementsTable: renamed appendToTable to load, and made it so
that it can be invoked as a static method of the prototype.

Also made it use utils.js parseArbor.
Circuit graph plot: anatomy is now computed locally from Gaussian-smoothed
arbor and includes the segregation index as concieved by Casey Schneider-Mizell.
Fix minor whitespace indentation issue.