Initial add of the generic optimizer code

Before digging into this code, look at the Rules implemented at the bottom of DagOptimizer.

There are several TODOS here:

- [x] After I split the code into separate files, I started hitting a scala 2.9 compiler bug, that I don't hit in 2.10. I'll try to work around, or possibly hope that Twitter finally gets on 2.9 before we need this.

- [x] Tests tests tests. I played around at the repl, but clearly we need super hardcore tests for any optimization framework.

- [ ] Actually call this code from an existing platform.
I think - does not need it.

I think + does need a type parameter because we are saying that `K[T]` and `V[T]` share the same type. That said, another question is your question from before: do you need `V[T]` here or would `T` do?. I think it probably could be rewritten in that way.