Improved offline updates theme support
This merge-req adds a number of improvements to the core and to the two-step plugin which together implement the offline-updates theme design from: https://wiki.gnome.org/Design/OS/BootProgress
This merge-req adds a number of improvements to the core and to the two-step plugin which together implement the offline-updates theme design from: https://wiki.gnome.org/Design/OS/BootProgress