Remove passing rootNode to lifecycle methods

[chenglou]

Referring to #276:

I think we should remove the rootNode being passed to componentDidMount and componentDidUpdate. For two reasons:

1. It's unnecessarily touching the DOM. This makes the separation of React and DOM harder, something I've seen being discussed.
2. It's inconsistent with other lifecycle methods such as componentWillUnmount. Since we're not adding rootNode to it due to reason 1, the only way to stay consistent is to remove it for the other two methods.
3. It makes adding new arguments harder in the future.

[sophiebits]

+1. Also makes it more annoying to add new useful arguments if there ever are any.

[chenglou]

Ops, added.

[petehunt]

Bump, this is about to bite us with the next github sync since we added a param to componentDidUpdate(). I think we should remove this in 0.6 @zpao

[vjeux]

We still need to document it :)

[chenglou]

I'm actually doing it that's why!