- 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
* add packages for EasyBuild and dependencies
* fix remarks w.r.t. docstrings & download urls, make dependency specs stricter w.r.t. required versions
* fix easybuild-* dep specs, should be open-ended
* correct dep specs for easybuild and easybuild-easyconfigs using @3.1.2[:]
