implemented ellipsoid scaling with equivalent masses.  resolves #603

resolves the unhelpful scaling of the standard inertial ellipsoids.
draws each inertial ellipse as if the link was an ellipsoid of a known constant density.  now you can actually see the inertial effects of each joint, e.g. on Atlas:

![2014-12-10-viewer 00](https://cloud.githubusercontent.com/assets/6442292/5375590/d9c41390-8039-11e4-883e-696a485af508.png)