Recommend exporting `propTypes` as a named export
Recommend exporting `propTypes` as a named export

By exporting `propTypes` as a named export *as well* as attaching them to the "class", they can be explicitly imported by tests and other components in a way that aligns with the future ES6 module dependency graph, rather than as an arbitrary property that isn't statically verifiable. Doing both is great imo.

Thoughts?
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