Breaking Change: No more require('*.css') in exported components

This is a breaking change release that addresses issues discussed in #50.

If you are migrating from a pre 0.4.0 release, you only need to make changes to your code if you were using the <Gallery /> component. If you are using <Gallery />, you must now explicitly load/import the gallery.css file.

For example, if you are using Webpack or another bundler that is configured to allow CSS files to be imported, you will need to include be sure, in addition to the gallery.js file, you also `import 'react-fine-uploader/components/gallery/gallery.css'.

If you are not using Webpack or a bundler, or if you do not want to or are not able to use ES6 imports to load CSS files, you must load the gallery.css file using a <link> tag instead.