- point to main Calamares site in the 'part of' headers instead
of to github (this is the "this file is part of Calamares"
opening line for most files).
- remove boilerplate from all source files, CMake modules and completions,
this is the 3-paragraph summary of the GPL-3.0-or-later, which has
a meaning entirely covered by the SPDX tag.
- the translations generated from public-domain files are CC0-1.0
- the files derived from Unicode tables are close to CC0-1.0,
possibly except that there is a FileCopyrightText line
- the scripts are BSD-2-clause,
- the generated files are CC0 (I'm not *100%* sure about the
derived file CountryData_p.cpp, which lists countries and
country codes -- it **is** extracted from CLDR data which
is not CC0)
