dlilien/elmerfem: SpecFab Coupling

Contains code and testing for interface with SpecFab, @nicholasmr's model of ice-crystal fabric development. Inclusion of the relevant solvers can be activated using -DWITH_SpecFab during compilation; the environment variable SpecFabROOT must point to the folder containing libspecfab. SpecFab must be version 2022.12.03 or higher, and the shared-library version must be compiled (this is done by default by compiling with make all for that repository). Tests for these new solvers (which can be used as examples) are found in folders SpectralFabric, SpectralFabricCoupled, and AIFlowSpectral in the elmerice/Tests folder. For real applications, it is probably best to start from the coupled test and adapt from there