Started writing a box manipulator.

The box manipulator is a drop-in for the pr2 manipulator node, but is designed
to work on boxes and is designed for Abby's parallel plate gripper.

So far:
* Written all the callbacks
* Written all the task queuing

Still to do:
* Calculate approach vector from bounding box parameters
* Calculate pregrasp position from approach vector
* Calculate final grasp position from pregrasp position
* Put in all the necessary python imports
* Test everything
* Modify launch files
* Modify object_manipulation_controller to call these services