LCM: begin work on stabilized fem for linear tets

First thing is to set up a benchmark test. Right now this is just hyperelastic
behavior.
LCM: initial work on stabilized fem in the Mechanics Problem
LCM: hook up stabilized pressure DOF in the Mechanics Problem
LCM: get stabilized pressure working
LCM: clean up and add a test for stabilized pressure

This is pretty neat, much more testing to do here.

For anyone interested, take a look in the StabilizedTet4 test directory for
an example for how to turn it on.

Note: this doesn't work yet for the linear elastic material, nor does it work
yet for surface elements. Each of those should be relatively easy extensions.