- rrt.py does not create client to gepetto-gui
  - rrt.py, grasp_ball.py, and grasp_ball_in_box.py reset problem at start.
  - create client to gepetto-gui in a separate command,
  - use widgets in gepetto-gui for displaying path and constraint graph
    instead of python commands.

  - make script common.py reentrant,
  - call hppcorbaserver even in manipulation,
  - use v (and not r) for viewer,
  - regerenetate html files.

  - replace box by sphere.

  - initialize graph,
  - use class Constraints to set the constraints,
  - update PathPlayer.

  - Add documentation of useful methods,
  - split Exercise 2 in two parts.

    - edge "release-ball" does not contain "placement" constraint.