Simplify Material Fitting Process

[bcerjan]

As it stands coming up with material fits is at best sort of confusing. It uses both Matlab and Mathematica and can still produce fits that cause the simulation to become unstable.

• Update to include Levy estimation of initial parameters in Mathematica (or do the advanced fitting in Matlab, either way works).

• Try to establish criteria that ensure stability of a material model in the simulation. This might be an entire PhD though, so don't get too caught up on it.