add model-inertia-check.l

Add program for checking inertia
and visualize inertia (see pic)
![samplerobot_inertia](https://cloud.githubusercontent.com/assets/2408164/4663104/40f72318-5538-11e4-84c2-b100d7674573.png)
Pink box is located at center of mass, rotate along principal axes of inertia, box size is calculated by inertia and mass, with uniform density and equivalent inertia