refactor(sub components): export at the top level

[nicolo-paganin]

The module is not working with the optimization module Babel transform-react-inline-elements.

The reasn is this one https://github.com/thejameskyle/babel-react-optimize/issues/19.

In order to get it working you have to import directly the submodule. For example for the Menu component

import Menu, {MenuItem, MenuMenu, MenuHeader} from 'stardust/dist/collections/Menu/Menu'

This is not working in this moment becase the submodules are not exported.

The proposed modification is to export also the submodules like this (dist/collections.Menu/Menu.js:182):

`
Menu._meta = _meta;

Menu.autoControlledProps = ['activeIndex'];
exports.Header = Menu.Header = _MenuHeader2.default;
exports.Item = Menu.Item = _MenuItem2.default;
exports.Menu = Menu.Menu = _MenuMenu2.default;
exports.default = Menu;
`

Thanks

[levithomason]

I'd accept a PR for exporting sub components. Should be rather easy, just add them to each index.js file in src/* folder.

There may be some automated testing considerations to update that I'm not seeing.

[levithomason]

Released in stardust@0.47.1, cheers!