Collection View Reset Bug

I noticed with the introduction of `removeChildView` in rc3 that it was possible to create a zombie empty view.

When the collection is reset with empty data, calling `closeChildren` would cause `showEmptyView` to be called multiple times through `removeChildView`.  Additionally, in `closeChildren`, I believe the call to `_initChildViewStorage` was causing the parent view to lose a reference to that empty view, which `children.length === 0` confirmed for me.

I hope this fix works.

Thanks for such an awesome library!