Adding support for PhantomX Pincher arm

I've tested this successfully with PhantomX Pincher.  (Also requires new config/URDF in Turtlebot which I've pushed to Corot).
I would suggest making ParallelConvert instance a member of the joint, and defining a new function "getPosition" or similar, which contains this if/else logic internally within the joint. This will avoid modifying the publisher class, and also avoid introducing some tight coupling between joint/publisher.