Extend with-data-prefetch to handle advanced use cases

[shalzz]

Adds a prefetch function inspired by https://github.com/zeit/next.js/tree/canary/examples/with-data-prefetch to allow prefetch on mouse hover and other advanced use cases (maybe include in that example itself?).

Based off of work done at #3457 for using getDataFromTree on the client which enables this by leveraging the getInitialProps functionality.

[sergiodxa]

@shalzz awesome idea but I don't think this should be tied to Apollo, instead improve the prefetch example to add this use case for onMouseOver, the examples are easily combinable if you read them.

[shalzz]

@sergiodxa adapted the PR to be specific to the with-data-prefetch example and be agnostic of other examples.

[sergiodxa]

Amazing!

[shalzz]

Merge this?