- 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.
Fixes CAL-345.
Changing group of home dir to the default "users" group might be a security risk
because every user which belongs to the default "users" group
might be able to access private data on home dirs of other users.
