Addition of new appstream-glib library. Part of GNOME 3.14 stack,
but as it is new, it does not hurt to already push it now to
Factory... so we have it in time.

@coolo: this package actually contains appstream-builder: just like createrepo,
you can run it against a directory full of RPMs and it extracts a valid
appstream.xml.gz (plus icons) from it, which we should get published in our repo metadata
(for gnome-software and potentially other appstream based software centers).

Once this is in place (currently, there is a hack in place for Factory, but only based
on .desktop files, ignoring the actual shipped appdata.xml files), we will need zypper
to have a hook to perform appstream-util install and enjoy the powers of it.