Add Planescape Torment and Baldur's Gate

Hello, I packaged up two old isometric RPGs, they seem to start, work and are perfectly smooth and stable (from my few minutes of testing), even tried multiplayer.

The one ugly thing is that it requires quite an old version of OpenSSL which can only be found in guix-past, I hate to add a whole channel, there might be ways around adding it globally, but that might even seem more ugly than adding it, besides while packaging old games other people might find it useful as well eventually.

Cheers and thank you for your work.