MS_brow_chev_decomp
Apply a decomposition of the elasticity tensor C, after: Browaeys and Chevrot (GJI, v159, 667-678, 2004)
Assumes that C is in its optimal orientation for decomposition
[Ciso] = CIJ_brow_chev_decomp(C) Isotropic projection of the elastic tensor.
[Ciso,Chex] = CIJ_brow_chev_decomp(C) Isotropic, and hexagonal parts of the elastic tensor
[Ciso,Chex,Ctet,Cort,Cmon,Ctri] = CIJ_brow_chev_decomp(C) All parts of the elastic tensor