Convert license headers to SPDX statements
Convert license statements to SPDX and add license text files in LICENSES folder as required by the REUSE specification.
Done by using licensedigger for the raw work, then manual tweaking.
@hein @psn @argonel @buschinski
@cordlandwehr Open question: at the bottom of file src/viewer/osd.cpp there is a code snippet "Code copied from kshadowengine.cpp" which has some separate licensing. Have I converted that correctly, any general comments on such copies with own separate license?
Edited by Friedrich W. H. Kossebau