Add spack package for TVB (tvb-library and tvb-data)

First version of spack packaging for the tvb-library (TVB simulator code) and tvb-data (demo data used by tvb-library).

Spack specs:

spack install tvb-data
spack install tvb-library^binutils+ld+gold%gcc@10.3.0  

The variant ^binutils+ld+gold is needed for llvm library brought by py-numba - which is a direct dependency of tvb-library.

Any suggestions are welcome.