dlg-package-installer.c: Remove X11 dependency
When a user opens an archive of a type that no installed package can open a dialog pops up with the option to search for a suitable application in GNOME Software.
This functionality was provided by org.freedesktop.PackageKit.Modify's InstallPackageNames method that required an X11 window id.
The fix consists of migrating to the new org.freedesktop.PackageKit.Modify2 D-Bus API that handles this use-case without needing an X11 window id and instead using a reverse domain name application id.
Closes #78 (closed)