Add gaming support

[mijofa]

1. Add a launcher for Steam Big Picture mode.
   • This requires finding a good WM to use, Steam fails badly with ratpoison.
   • This project has likely done everything upmc needs: https://github.com/thor27/steam-login
2. Either add all your other games via the Steam menu, or put an interface in UPMC for arbitrary Linux games.
3. Add support for emulators
   • Preferably this would be interleaved with the arbitrary games so that the user can't tell, but without needing to write a separate script for every single rom.
   • It may end up being easier to write a separate script for each rom and treat them as arbitrary games due to a significant amount of config differences between each rom.