[opensuse-marketing] wiki pages updated

Heya all, I have updated the following wiki pages to the current state of affairs (we do most of our things in GitHub): http://en.opensuse.org/openSUSE:Marketing_and_Artwork_repository http://en.opensuse.org/openSUSE:Marketing_materials http://en.opensuse.org/openSUSE:Artwork_posters http://en.opensuse.org/openSUSE:Presentations http://en.opensuse.org/openSUSE:Buttons_and_banners Reviews would be welcome :D