feature/story wrapper

[kevindavi5]

This PR addresses issue #2 by extending the docz-plugin-storybook config to accept a story wrapper.

// doczrc.js
import { storybook } from 'docz-plugin-storybook';

export default {
  plugins: [storybook({ wrapper: './story-wrapper' })]
};

• wrapper accepts a path to a component that will wrap each story
• if no wrapper is passed we use a default wrapper
• basic docz example updated to wrap each story with an iframe
• included example with custom styles passed to wrapper

TODO: (recommend future iteration)

• figure out how to play nice with css-in-js libs when isolated

NOTES:

• tested a styled-component and found that react-styled-frame didn't work :/
• error occurred from react-styled-frame hack of copying in document.head.innerHTML
• recreated react-styled-frame locally and was able to get it to render but styles were missing

A couple thoughts:

• issue may be from may be from multiple instances of styled-components (warning in console - doubtful) -- two instances of styled-components.browser.esm.js, //webpack & //webpack-internal
• issue may be from StyleSheetManager not talking to FrameContextConsumer (likely) -- tried creating a separate ref as a target for StyleSheetManager to no avail

[transitive-bullshit]

@kevindavi5 I moved your readme additions into #12 and #13 respectively.

[transitive-bullshit]

@kevindavi5 looks like the CI failure is related to the webpack snapshot being out-of-date.

I'm going to merge as-is, then update snapshots locally, then we should be stable.