Adds rootHeirarchies to the storybook config
Allows us to section off the stories into groups to match https://design.gitlab.com/
Instead of just passing the name of the component to documentedStoriesOf
we can pass a hierarchy like this documentedStoriesOf('regions|empty-state', readme)
. Any stories without a set group will live in the root.
It also configures all the exisiting stories to use the newer format.
Closes #119 (closed)