Fixed dilatation rate calculation, added option of using 2D strain rate invariants and removed some commented lines

Removed passing of call_cnt for debugging, extra debugging output, added option of using 2D strain rate invariants and fixed Mohr-Coulomb plasticity formatting to be similar to the other options

Modified to use an initial e2d value for the first plasticity calculation and output the dilatation rate

Modified nonlinear iteration convergence criterion to calculate the maximum velocity difference between iterations over the maximum vector length from the previous iteration