Add bower.json & optional AMD support

This PR:

* Adds [Bower](http://bower.io/) support. I didn't publish it to the registry, but you can now at least point Bower at the Git repo.
* Adds optional AMD support. This is *required* for this mixin to work when React is loaded through AMD, since no global `React` namespace is available.

If either commit proves controversial, I'm happy to cherry-pick one into a separate PR, but hopefully these are agreeable changes :)