Now all the business logic is in Config, the door is open to
building a QML-ified netinstall module. I'm not sure that
would be worth it: packagechooser offers more space for a
nice UI and should be QML'ed first.
- gcc (up to at least version 10) is worse at recognizing that all
cases have been handled, so it complains about all the switches
that cover enum values.
- both clang and g++ support __builtin_unreachable(); (as Kevin
Kofler pointed out) so we don't need the macro to do different things;
- the compilers have gotten better at detecting unreachable code,
so instead of inserting macros or fiddly bits, just drop them
and the unreachable code they comment.
- 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.
- Add initial definition of Config object, which will extract the model-
setting and loading code from the page, and which is also prep-work
for a QML version of this module.
- While here, remove superfluous code
