games: Add from-orbit.

This adds from-orbit, a game from itch.io. It works well, except I don't have any sound and some graphics are missing. The most important issue though is the download link: I wasn't able to find any way to automate the download from itch.io, so for now I'm relying on downloading the game manually and loading it into the store with guix download or with the --with-source option. Wdyt?