Merge branch 'add-spdx' into 'master'

.gitignore

.gitlab-ci.yml

CHANGELOG.md

CMakeLists.txt

INSTALL

LICENSES/LicenseRef-GPL-2.0-only-with-DUNE-exception.txt

README.md

cmake/modules/AddARPACKPPFlags.cmake

cmake/modules/AddSuperLUFlags.cmake

cmake/modules/CMakeLists.txt

cmake/modules/DuneIstlMacros.cmake

cmake/modules/FindARPACK.cmake

cmake/modules/FindARPACKPP.cmake

cmake/modules/FindSuperLU.cmake

config.h.cmake

doc/CMakeLists.txt

doc/blockstructure.eps.license

doc/doxygen/CMakeLists.txt

doc/doxygen/Doxylocal

doc/doxygen/mainpage.txt