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.
you can actually declare this as ```type IdSet[_] = Set[Id[_]]```. In type declarations iirc the ```_``` on the left sort of signals shape, not normal wildcarding. So this just says that the IdSet type takes one argument, but we actually ignore it.