Refactor StoryStore to be a separate package

[tmeasday]

So we can reuse it between the various app layers. It doesn't make sense to duplicate the .storiesOf() logic, and if we factor it out it's likely it can be used for other purposes.

[danielduan]

Is this still relevant? I feel like if we're gonna extract it as a package that we might as well refactor the thing and use redux or mobx.

[tmeasday]

Yes this is done in the form of @storybook/core 👍