calvin_pick_n_place: spinner, synchronous moves, less sleeps

* Added an AsyncSpinner; this fixes the problem that pick() doesn't return.
* Changed asyncMove() to move() so we wait until the previous move is complete.
* Removed a lot of unneccessary sleeps.
calvin_pick_n_place: use moveit group to open gripper instead of action

There's nothing wrong with the previous solution, but using the MoveIt
group is easier.
calvin_pick_n_place: use detachObject()
calvin_pick_n_place: remove attempt to allow collisions with testobject

* This doesn't work; it just messes up the planning scene, leading to
  aborted plans because of collisions with the object when retreating.
* One should never construct a planning scene directly; instead, use the
  Planning Scene Monitor (see
  http://docs.ros.org/api/pr2_moveit_tutorials/html/planning/src/doc/planning_scene_tutorial.html#setup)
calvin_pick_n_place: place now works!