Update React to v15?

[novacrazy]

React has undergone significant improvement in the last year, and it's worth investigating if newer versions of React and Marko affect the benchmarks.

[patrick-steele-idem]

I took an initial look and I am seeing performance improvements with React 15.0, but it is still significantly slower on the server compared to Marko. It'll take a little longer for me to update the results with the client-side benchmarks because it requires manually running in each browser, but here's a quick peak at how React 15.0 compares to latest Marko/Marko Widgets: