Flux todomvc enhancements from justin

2 minor changes:

1. Enable react chrome dev tools.
2. Smaller methods.
Agreed with zpao here - I prefer the original explicitness. Returning the calculated result in helper methods instead of storing it in this._something would be better too (and then they can be pulled to the top of the file as anonymous functions), but I'm not sure the extra indirection is worth it for this example case