[Data-modeling] Mod addition to Computer Games domain

[Tadhg O'Higgins]

I'd like to propose adding Computer Game Mod as a type to the Computer 
Game domain, and Mods as a property to Computer Game.

Mods are (usually) fan-developed modifications to published games, 
classic examples being the original Team Fortress and Challenge ProMode 
Arena (both mods for Quake-engine games).

The data implications are fairly simple. Computer Game gets an extra 
property that expects Computer Game Mod as its value, and Computer Game 
Mod is a new type in the domain that is co-typed as a Computer Game and 
also has a single property of its own, Game Modded, which expects 
Computer Game.

Examples of this from sandbox:
New schema: http://sandbox.freebase.com/tools/schema/cvg/computer_game_mod
A mod: 
http://sandbox.freebase.com/view/guid/9202a8c04000641f8000000006ef2906
A game with a mod: http://sandbox.freebase.com/view/en/quake_iii_arena

Suggestions welcome. If there are no objections, I'll probably push this 
to live in a week or so.

Tadhg