[license] add license files and AUTHORS.md
[license] update to GPLv3 or later
[license] bulk license .input, references, .msh, figures, documentation
[license] bulk license .fig images with CCBY-4.0
[license] add CC-BY-4.0 SPDX headers for .tex files
[license] add CC-BY-4.0 SPDX headers to .bib files
[license] add CC-BY-4.0 SPDX headers to .dgf files
[license] add CC0-1.0 SPDX headers to repository files
[license] add GPLv3-or-later SPDX header to .hh, .cc, CMakeLists.txt
[license] add GPLv3-or-later SPDX headers to scripts
[license] add GPLv3-or-later SPDX headers to module files
[license] remove current license statements
[license] replace old license
remove stamp-vc file