nautilus: add 3.12.2 version and add tracker support
dconf: add 0.20.0 version
sushi: add 3.12.0 version
zenity: add 3.12.1 version
gnome-keyring: add 3.12.2 version
libzapojit: use gnome mirror
Allow specifying the gnome3 packages to use for the xserver service