Packages, software centers, and AppData

It'd be better for this article to make the distinction between GNOME PackageKit, a collection of GUI tools like the package installer and package updater, and PackageKit, the package abstraction layer used by GNOME PackageKit, GNOME Software, Apper, and soon Muon. GNOME Software requires PackageKit to function; the model is solid and here to stay. GNOME PackageKit is what we're hoping distros will drop.