In spite of there being considerable documentation sometimes in the
config file, we go with CC0 because we don't want the notion of
'derived work' of a config file.
The example `settings.conf` is also CC0. Add some docs to
it while we're at it.
- Since the package chooser might be used more than once, or for
more specific items than "Packages", introduce a way to provide
specific strings for display.
- The only string needed is the ViewStep name, since the item with
id "" can be used for the no-selection item.
- Use *appstream* as key in one of the items for the package-
chooser to load data from the AppStream cache in the system.
- Usable for some applications; for DE-selection not so much.
- Currently unimplemented.
- Using id's as keys in a map orders them indeterminately -- in
practice, alphabetically by key. Switch to a list form so that
the products stick to the order they have in the config file
(which means distro's can list "preferred" versions at top).