[Flatpak] Bundle more chess engines inside the flatpak
No engines installed in the base system are displayed when starting gnome-chess in flatpak format. Tested in fedora 27.
Tip: It will be nice to include some extra engines in the flatpak version of gnome-shess like Stockfish. This would help a better discovery by novice users or for whose systems it is difficult to install extra software (eg EndlessOS)
Edited by Bastián