Add Jacobian debug script

As explained in #4144 this adds the Jacobian debug script. I tested it on a few of the built-in kernels, and received clean ```No errors detected. :-)``` messages. 

There are a quite few edge case which this does not handle well yet:
* huge file meshes (Or anything that is not a generated mesh and cannot be easily resized)
* mixed element types and orders

 But I think this is already more useful than having no such capability.
This will almost all go away in the next version (the code already exists on my machine and is just waiting for the prerequisite DOFMap stuff to get merged).