Add post-select hook

Although react-tabs has onSelect, which is called when the tab is about to change, I see no post-update hook.

My requirements for this are that, I have to do some post-processing on the rendered DOM. On the parent component that I use react-tabs in, I do the post processing of parent component in its componentDidUpdate method but obviously the updates on the child (react-tabs in this case) doesn't trigger the post-update method of the parent.

It would be useful for me if there was a post-update hook on react-tabs.

Note: I can fix this by using the controlled-mode. Therefore feel free to close the issue if this looks like an unsuitable feature request.

Start by comparing the existing onSelect callback with controlled-mode behavior and React's componentDidUpdate timing. Determine the intended post-update hook contract and how it should behave during tab changes. Done means the feature scope is agreed and its callback behavior is covered by tests and documentation.