Bug#860427: nestopia; Add metadata for integration with gnome-games-app, gnome-software

[Jeremy Bicha]

Package: nestopia
Version: 1.47-2

gnome-games-app is now in Debian unstable. (It will not be in
stretch.) It can use libretro cores like nestopia if there is a
.libretro file describing it.

gnome-software can show nestopia as an Addon for gnome-games-app if
nestopia includes appstream metadata for that.

I am attaching a patch in the next email that I successfully applied
on Ubuntu 17.04.

References
----------------
https://wiki.gnome.org/Apps/Games/Documentation/LibretroDescriptorSpec
https://bytesgnomeschozo.blogspot.com/2017/03/gnome-games-324.html
http://www.omgubuntu.co.uk/2017/04/retro-tastic-gnome-games-makes-ubuntu-17-04

Thanks,
Jeremy Bicha