added controlledItemIndex so the central can be controlled by parent

[ganmor]

Sorry for not getting back earlier about the previous pull request, and thanks for integrating the changes.
This pull request allow the carousel to be controlled by the parent component and thus the url.

Also do you have any thought on how to implement a scroll method that takes velocity / animation duration as parameters ? ( if the scroller is going to be controlled by the url it would be much more convenient to have those exposed )

[roeierez]

I like the use of componentWillReceiveProps.
I think we don't need two 'controlled' indexes, we can use the 'initialItemIndex' also as you suggested in 'componentWillReceiveProps' and it will let the user scroll to an item on mounting and also whenever he changes the props.
If you think like me and willing to do these changes I will merge it as is.
Let me know what you think, and thanks again.

[roeierez]

Regarding controlling the animation duration.
Currently there is a constant in the scroller called: SCROLLING_TIME_CONSTANT
as higher it is as longer is the animation. you can expose it as props in the carousel and propagate it to the scroller.

[ganmor]

I will submit a PR.
What I am thinking about when talking about scrolling animation is something like this.

  componentWillReceiveProps: function(newProps, newState) {
            if (newProps.controlledItemIndex && newProps.controlledItemIndex !== this.props.controlledItemIndex) {
                this.refs.scroller.scrollWithAnimation( (this.getItemWidth() + this.getItemsSpacing()) * (newProps.controlledItemIndex || 0) );
            }
        },

notice the scrollWithAnimation.

Thanks for the answer anyway, I will try to submit a different PR with a possible solution for the scrollWithAnimation.

[ganmor]

PR updated