- 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 build instructions are not that interesting, it's a toss-up
between CC0 and BSD-2, but because other CMake bits are BSD-2-Clause,
apply that to more CMakeLists. The copyright date isn't all that
accurate, but these are just inconsequential files.
While here, tidy up and get rid of some useless intermediates.
This is orthogonal to the SKIP_* mechanism already documented
for avoiding modules. If the module is enabled, but its dependencies
are not present, don't bother building the module. This follows
e.g. plasmalnf as an "avoidably heavy dependency".
Related to a misplaced comment in ISSUE #956
