[Data-modeling] 3 proposed properties for computer game engine

[Tadhg O'Higgins]

Engine Family (e.g. the Quake and id Tech 2 engines are both part of the 
id Tech family)

Predecessor Engine (e.g. the Unreal Engine 2 is the predecessor to the 
Unreal Engine 3)

Successor Engine (e.g. id Tech 3 is the successor to id Tech 2)

I've implemented this on sandbox, and a sample (not very interesting) 
view can be seen here:
http://sandbox.freebase.com/view/cvg/views/id_tech_engines

If there aren't any objections, I'll implement this in production this week.

Tadhg