* update to kim-api-2.1.1 and openkim-models-2019-07-25
* openkim-models provide needed dependency constraints and settings
* add maintainers and fixup flake8 errors
* Replace kim-api package with kim-api-v2, which has different
versions and removes the 'cmake_args' method
* Add openkim-models-v2 as an extension package
- 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
