add virtual function resetConstraints to deal with collisions.
  add virtual function addConstraintToConfigProjector to deal with gripper
  disable collisions in the ProblemSolver.

Add map of grasp (=pair<gripper,handle>) to disable the collisions between gripper and handle when a grasping constraint is set.

Add function getDeviceNames in robot to get the names of robots and object in the same order than in the configuration.

Add collisions between devices when buildcomposite robot and also deal with the disabled collisions of grippers.

  rename handlePositionInJoint as objectPositionInJoint.

  - Handle includes a virtual method to define a grasp constraint
  - add a class AxialHandle that derives from Handle and that creates grasp
    constraints with free rotation around the x-axis of the handle.

  - when copying a joint, copy relative position in parent joint. Thus do
    not recompute it when adding child joint.

  - first joint was wrongly recovered.

  - map has been trasferred to core::ProblemSolver.

  - constraint -> numericalConstraint.

  - fix documentation.

  return os at end of function.

  - TypeWkPtr -> TypeWkPtr_t.

  - build kinematic chain in Robot::init so that weak pointer to instance is
    already created,
  - attach joint to parent before attaching children.