- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
- core and most packages are (Apache-2.0 OR MIT)
- a very small number of remaining packages are LGPL-2.1-only
* update of veloc & dep versions (replace old non-working versions)
* veloc doesn't work with gcc <= 4.9.3
* explicitly pass MPI to CMake for veloc build