Fix bug in object iterator

  if first body has no object, iterate on following joints.
Fix bug in Rotation joint interpolation and distances.
Merge remote-tracking branch 'origin/master'
change manipulation::gripper to model::gripper
Merge branch 'gripper' into Mathieu
Add gripper.cc and gripper.hh
Rename handlePositionInJoint as objectPositionInJoint.
Merge remote-tracking branch 'origin/master'