Support disabled, aborted, and never run jobs

In addition to cleanly supporting these other job types, this pull request also updates the stats rollup to only display fields that have a non-zero value.

This is based on GH-36.
I went ahead and merged this, but note that 'unstable' wouldn't be a job state in this context; unstable would be build health/stability, which we already use to display glyphicons being displayed next to the build name / URL.