Expose React.addons.* as react/addons/* on npm and deprecate react/addons

[sophiebits]

The current system of packaging react/addons isn't great because you need to pull in all the addons even if you just want to use one of them. Instead, let's make it so you can do require('react/addons/TransitionGroup') and similar.

This should be as simple as adding a few files to build/npm-react that require the (private) internal modules.

// npm-react/addons/TransitionGroup.js
module.exports = require('../lib/ReactTransitionGroup.js');

[zpao]

cc @gaearon @iamdustan. This came out of the Twitter discussion as a possible way to start migrating to requiring of a single addon in a condoned way (without reaching directly into lib/) that shouldn't screw up other packaging.

[pspeter3]

This would be greatly appreciated.

[gaearon]

Sounds like a good plan to me!

[iamdustan]

@zpao @spicyj should I update the docs with this change as well?

[sophiebits]

Please do!