1506 incompressibility cauchy green policy

Contains a new CauchyGreenPolicy to be used by the quasi incompressible version of the SecondPiolaKirchhoff operator which dictates whether or not the same CauchyGreen operator should be used for both the volumetric and deviatoric parts of the computation or if a different one should be fed to each. When a different Cauchy Green is provided to each part, this allows for more flexibility in choice of the time scheme for dynamic problems. See the HyperelasticityIncompressible model for a use case where the time scheme in the volumetric part is only written for the current value whereas the deviatoric part is computed at the midpoint.