- 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.
- CC0-1.0 for the uninteresting version-headers
- GPL-3.0-or-later for the services
- add SPDX identifiers to Calamares C++ libraries and application sources
- add SPDX identifiers to Calamares QML (panels and slideshow)
- the `qmldir` is a list of names of things in the directory,
so CC0-1.0 it as "uninteresting"
- QRC files are lists of names of things in the directory,
so CC0-1.0 them as well
