Fixes to the PhysX engine.

- Corrected segfault due to infinite recursion
- Corrected undefined reference due to abstract method left erroneously in CPhysXModel
- Better method to update the origin anchor of the single object model class
- Removed shape list in that class, because it was useless
- Added comments to that class
- Fixed box and cylinder model to reflect the changes
Minor fixe
Fixes to the tests
Added a first draft of 3D model for the e-puck.

The model is largely incomplete. It will be used to prototype the multi body model of PhysX.