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.
Hmm, a little duplication here...  Is there a better way?