Split up the store loading so that stores are created in a predictable order
Split up the store loading so that stores are created in a predictable order

This allows us to prioritize store items of the same type, prefering items
added to the store first. This means we can avoid merging AppStream files
provided by both PackageKit and by xdg-app, as this does not work well at all.

hughsie/appstream-glib,ximion/appstream-glib,ikeydoherty/appstream-glib,ximion/appstream-glib,ikeydoherty/appstream-glib,hughsie/appstream-glib,hughsie/appstream-glib,ximion/appstream-glib