Generalize the input for the elastic constants
Per the 8/14/20 meeting, we decided that it would be best to allow users to input the full 21 elastic constants to define an arbitrary anisotropic material. This would be in addition to the current more structured approach where the user input a symmetry and a collection of nonzero constants.
This is similar to how it is done in PRISMS-PF (see the bottom of this page).