New wallpaper for crimson

It would be nice to have updated wallpapers in place for when we release crimson

/cc @francois.techene

I think that @tobias.bernard will agree with me on this but I think that the best experience with GNOME comes from using GNOME's wallpapers. They are awesome and they are part of overall GNOME experience with each release. Especially since support for single dark + light changing wallpapers.

If we want to differentiate ourselves we may just take the main default wallpaper shipping with the version of GNOME at the time of shipping Crimson and give it the Crimson color touch.