RankFourTensor documented and slightly refactored to make various methods protected.
RankTwoTensor doxygen doco slightly enhanced.
RotationTensor doco very slightly enhanced.
ElasticityTensorR4 streamlined to remove various operations already defined in RankFourTensor, and doco enhanced, and cosseratElasticJacobian renamed to elasticJacobianwc.
All these four classes moved from materials to utils.