Keep track of collisions and distance body pairs.
Make methods Joint::computePosition and Joint::recursiveComputePosition const.

  - make internal compuation members mutable.
ObjectVector_t is now a list of CollisionObjectPtr_t.
Keep track of obstacles in class Device.
Cosmetic change.
Add forward declarations for anchor joint.
When creating a collision object, set positionInJointFrame_ to global position.
Add a function to write a configuration in a string.